As filed with the Securities and Exchange Commission on November 7, 2017May 4, 2022

Registration No.          333-

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C.WASHINGTON, DC 20549

FORM S-3

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

Aspen Aerogels, Inc.

(Exact name of registrant as specified in its charter)

The information in this preliminary prospectus is not complete and may be changed. changed without notice. The selling stockholders named in this prospectusshareholder may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This preliminary prospectus is not an offer to sell these securities and the selling stockholdersshareholder named in this prospectus areis not soliciting an offeroffers to buy these securities in any state where the offer or sale of these securities is not permitted.

Subject to completion, dated May 4, 2022

PRELIMINARY PROSPECTUS

6,344,585 Shares of Common Stock

This prospectus relates to the offer and sale by the selling shareholder identified in this prospectus, and any of its pledgees, donees, transferees, or other successors in interest, of up to 6,344,585 shares of common stock of Aspen Aerogels, Inc. (the “Common Stock”), which consists of (i) up to 4,552,599 shares of Common Stock issuable upon conversion of Convertible Senior PIK Toggle Notes due 2027 issued to the selling shareholder (the “Notes”) or pursuant to any other term of the Notes, including as a result of any of the payment-in-kind (“PIK”) provisions, and (ii) up to 1,791,986 shares of Common Stock sold to the selling shareholder pursuant to that certain Securities Purchase Agreement, dated as of February 15, 2022 (the “SPA”).This prospectus covers any additional securities that may become issuable by reason of stock splits or dividends.

We are filing the registration statement of which this prospectus is a part at this time to fulfill contractual obligations to do so pursuant to a securities purchase agreement and note purchase agreement, as further described in this prospectus. We will not receive any of the proceeds from the sale of the Common Stock by the selling shareholder.

The selling shareholder and its pledgees, donees, transferees, or other successors in interest may offer the shares of Common Stock in one or more transactions at fixed prices, at prevailing market prices at the time of sale, at varying prices determined at the time of sale, at negotiated prices, or in trading markets for our Common Stock. Additional information on the selling shareholder, and the times and manner in which it may offer and sell shares of our Common Stock under this prospectus, is provided under “Selling Shareholder” and “Plan of Distribution” in this prospectus.

Our Common Stock is quoted on The New York Stock Exchange under the symbol “ASPN.” On May 3, 2022, the last reported sale price of our Common Stock was $22.78 per share.

Investing in our Common Stock involves certain risks. See “Risk Factors” beginning on page 3 of this prospectus for the risks that you should consider. You should read this entire prospectus carefully before you make your investment decision.

NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE SECURITIES COMMISSION HAS APPROVED OR DISAPPROVED OF THESE SECURITIES OR DETERMINED IF THIS PROSPECTUS IS TRUTHFUL OR COMPLETE. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

The date of this prospectus is                 , 2022

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ABOUT THIS PROSPECTUS

Except where the context requires otherwise, in this prospectus the terms “Company,” “our company,” “Aspen,” “we,” “us,” and “our” refer to Aspen Aerogels, Inc., a Delaware corporation, and, where appropriate, its direct and indirect subsidiaries.

You should rely only on the information contained or incorporated by reference in this prospectus. We have not authorized any other person to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it. For further information, please see the section of this prospectus entitled “Where You Can Find More Information.” The selling shareholder is not making an offer to sell these securities in any jurisdiction where the offer or sale is not permitted.

Subject to completion, dated November 7, 2017

PROSPECTUS

6,620,452 Shares of Common Stock

This prospectus relates to the offering and resale by the selling stockholders identified herein of up to 6,620,452 shares of our common stock, par value $0.00001 per share. These shares were issued to the selling stockholders by Aspen Aerogels, Inc. (“Aspen,” “we,” “us” or the “Company”) principally upon conversion of their shares of convertible preferred stock and convertible promissory notes into common stock in connection with our initial public offering of common stock in June 2014 (the “IPO”) or were purchased by certain of those selling stockholders in the IPO.  In addition, certain of these shares were issued to members of our board of directors at the time of the IPO as compensation for their service as directors. We are registering the resale of the shares issued upon conversion of convertible preferred stock and convertible promissory notes as required by the Sixth Amended and Restated Registration Rights Agreement that we entered into with the investors named therein, dated as of June 11, 2012, as amended (the “Registration Rights Agreement”). We will not receive any proceeds from the sale of these shares by the selling stockholders. The selling stockholders may sell the shares as set forth herein under “Plan of Distribution.” For a list of the selling stockholders, see the section entitled “Selling Stockholders” on page 11. To the extent required by the Registration Rights Agreement, we have borne and will continue to bear the costs relating to the registration of these shares.

Our common stock is listed on The New York Stock Exchange (the “NYSE”) under the symbol “ASPN.” On November 1, 2017, the last reported sale price of our common stock on the NYSE was $4.46 per share. The selling stockholders may sell all or a portion of their shares through public or private transactions at prevailing market prices or at privately negotiated prices.

We may amend or supplement this prospectus from time to time by filing amendments or supplements as required. You should read the entire prospectus and any amendments or supplements carefully before you make your investment decision.

We are an “emerging growth company” as defined under the federal securities laws, and, as such, are eligible for reduced public company reporting requirements. See “Prospectus Summary—Implications of Being an Emerging Growth Company.”

Investment in our common stock involves risks. See “Risk Factors” beginning on page 7 of this prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus. Any representation to the contrary is a criminal offense.

The date of this prospectus is ____________, 2017

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ABOUT THIS PROSPECTUS

You should rely only onnot assume that the information contained in this prospectus, incorporated by reference in this prospectus, or contained in any prospectus supplement or free writing prospectus filed with the Securities and Exchange Commission. Neither we nor the selling stockholders have authorized anyone to provide you with additional information or information different from that contained in this prospectus or incorporated by reference in this prospectus. The selling stockholders are offering to sell, and seeking offers to buy, shares of our common stock only in jurisdictions where offers and sales are permitted. The information containedappearing in this prospectus is accurate only as of any date other than the date on the front cover of this prospectus, regardless of the time of delivery of this prospectus or of any sale of shares of our common stock, and the information we have incorporated by reference in this prospectus is accurate only as of the date of the document incorporated by reference.a security. Our business, financial condition, results of operations, and prospects may have changed since those dates.

This prospectus contains trademarks, tradenames, service marks, and service names of the Company.

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SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

The SEC encourages companies to disclose forward-looking information so that investors can better understand a company’s future prospects and make informed investment decisions. This prospectus contains such dates. You should read both“forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995. These statements involve known and unknown risks, uncertainties and other important factors, which may cause our actual results, performance or achievements to be materially different from any future results, performances or achievements expressed or implied by the forward-looking statements. Forward-looking statements include, but are not limited to, statements about: the expected future growth of the market for our aerogel products and our continued gain in market share, in particular in the electric vehicle market, the energy infrastructure insulation market, the lithium-ion battery thermal barrier markets, and other markets we target; our beliefs about the competitive strengths and value propositions of our technology and our products and our ability to gain additional market share and enter into new markets based on those strengths; our expectation that our investment in incremental manufacturing and operating expense will sustain long-term growth in our existing markets and develop new business opportunities; our plans to continue to develop and optimize aerogel products for high-value applications within the sustainable building materials market and our plan to realize revenue from this market; our plans and expectations to partner with industry leaders in the battery and electric vehicle market or such partnerships resulting in products and technologies or otherwise resulting in meaningful financial results; our expectations about the size and timing of awarded business in the EV market, future revenues and profit margins, arising from our supply relationship and contract with automotive original equipment manufacturers, or OEMs, and our ability to win more business and increase revenue in the EV market; our pursuit of high-value opportunities for our aerogel products within different segments of the EV market, the global insulation market, including the sustainable building materials market, and our plans to leverage our aerogel technology platform to develop innovative, aerogel enhanced products for applications in new markets; our plans to focus additional resources to continue to grow our share of the EV market and the energy infrastructure insulation market; the current or future trends in the energy, energy infrastructure, chemical and refinery, LNG, sustainable building materials, EV thermal barrier, EV battery materials or other markets and the impact of these trends on our business; our investments in the electric vehicle market and aerogel technology platform; our pursuit of and the expected greater adoption of our products in the LNG and power generation markets and our expectation that product revenue will be generated in large part by demand for insulation associated with scheduled plant shutdowns, or turnarounds, and other maintenance-related projects; our expectation that our products will be specified during the design phase in a growing number of new plant construction and capital expansion projects and our expectation that we will have an increasing percentage of our products sold for use in capital projects; our expectation that the growth in global energy demand and EV market will result in increased new-build and large capacity expansion projects, driving demand for our aerogel products; our plans to continue our strategy of working with innovative companies to target and penetrate additional market opportunities; our plans to develop strategic partnerships to facilitate market penetration beyond the energy infrastructure and sustainable building materials market, as well as the expected goals and priorities of such strategic partnerships; our belief that an adequate long-term supply of silica-precursors and other raw materials is available and that our plans to reduce reliance on precursors susceptible to significant price fluctuations will be successful; our belief that we can strategically increase our capacity to meet the demand or that we will be able to make such capacity increases in a timely manner; our expectation in our ability to implement lower cost product formulations and realize material purchasing efficiencies; our belief that our portfolio of patents, trade secrets and know-how present a significant barrier to potential new entrants in the production of aerogel blanket insulation; our expectation that we will be successful in enforcing and defending our patents against competitors and that such patents are valid and enforceable, as well as our expectations about the costs and consequences of our current or potential future patent litigation and the potential for additional patent litigation; our belief that our products possess strong competitive advantages over traditional insulation materials, including the superior thermal performance and the thin, easy-to-use and durable blanket form of our products; our belief that we can finance the construction and development of our planned second manufacturing facility in Bulloch County, Georgia with anticipated available credit, cash flows from operations, debt financings, technology licensing agreements, customer prepayments or equity financings; our expectations regarding the investment to open a second manufacturing facility in Georgia

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and the anticipated job creation as a result thereof; the anticipated aerogel capacity expansion as a result of the planned second manufacturing facility in Georgia and the expected commencement of production; our belief that our end-use customers will continue to invest in major energy infrastructure projects; our expectation that we will continue to sell our products in the sustainable building materials and other end markets; our expectations that our work with partners will accelerate the commercialization of these carbon aerogel anode materials in the electric vehicle market; our belief that the potential for significant technological innovation in traditional insulation materials is limited and that new high-performance materials will be required to meet evolving market requirements for energy efficient insulation systems; our belief that our aerogel products and manufacturing processes are proprietary and that we can protect our patents, trade secrets and know-how associated therewith; our belief that we can continue to improve the cost efficiency of our manufacturing process, that our current expansion plans offer attractive returns on incremental invested capital, and that we will focus our development efforts on new products and next generation technology with application in new, high value market segments; our belief that we will have opportunities to address additional high value applications in the estimated $3.9 billion global insulation market, and that we are well-positioned to leverage a decade’s worth of research and development to design and commercialize disruptive aerogel products for a wide array of new markets; our belief that our products have the lowest cost on a fully-installed basis or offer significant life-cycle cost savings in energy infrastructure and certain other applications as compared to traditional insulation materials; our plans to continue to expand our global sales force and distribution network to support anticipated growth in customers and demand for our products and our plans to seek to promote greater enterprise-wide utilization of our products by existing end-use customers; our expectations and projections about future revenues, revenue growth, costs, expenses, production volumes, manufacturing productivity, gross profit, profitability, net loss, loss per share and Adjusted EBITDA, sources and uses of cash, liquidity, cash flow, capital requirements and the sufficiency of our existing cash balance and available credit; our expectations that most of our revenue will continue to come from a relatively small number of customers for the foreseeable future; our expectations of long-term revenue growth, with increasing levels of gross profit and improved cash flows from operations and our expectations that we will incur significant capital expenditures related to the expansion of our manufacturing capacity to support this expected long-term growth in demand; our expectation to continue to increase investment in research and development in our efforts to enhance and expand our aerogel technology platform; our expectations about the impact of new accounting pronouncements on our consolidated financial statements and related disclosures; our belief that our experienced and dedicated leadership team will provide us with a competitive advantage in the industry; our belief of our technological and market leadership in aerogels; the expected future development of new aerogel technologies; and our expectations about limitations of net operating losses.

Words such as “may,” “will,” “anticipate,” “estimate,” “expects,” “projects,” “intends,” “plans,” “believes” and words and terms of similar substance used in connection with any discussion of future operating or financial performance, identify forward-looking statements. All forward-looking statements are management’s present expectations of future events and are subject to a number of risks and uncertainties that could cause actual results to differ materially and adversely from those described in the forward-looking statements. These risks include, but are not limited to, those under the heading “Risk Factors” contained in Item 1A of our Annual Report.

In light of these assumptions, risks and uncertainties, the results and events discussed in the forward-looking statements contained in this prospectus might not occur. Stockholders and other readers are cautioned not to place undue reliance on the forward-looking statements, which speak only as of the date of this prospectus. We are not under any obligation, and we expressly disclaim any obligation, to update or alter any forward-looking statements, whether as a result of new information, future events or otherwise. All subsequent forward-looking statements attributable to Aspen Aerogels, Inc. or to any person acting on its behalf are expressly qualified in their entirety by the cautionary statements contained or referred to in this section.

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RISK FACTORS

An investment in our securities involves a high degree of risk. YouBefore making an investment decision you should carefully read and consider the risks and uncertainties and all of the other information, documents or reports included or incorporated by reference in this prospectus, and, if applicable, any prospectus supplement or other offering materials, including, without limitation, the risks and uncertainties discussed underrisk factors in the section entitled “Risk Factors” in our most recent Annual Report on Form 10-K, filed which is on file with the SEC, which are incorporatedas updated by reference, in this prospectus, and any updates to those risk factors included from time to time in our periodic and current reports filedsubsequent filings with the SEC and incorporated by referenceunder the Exchange Act. If any of the risks set forth in this prospectus. Ourour most recent Annual Report on Form 10-K or subsequent Exchange Act reports actually occur, our business, financial condition, and/or results of operations could be harmedsuffer. In that case, the market price of our Common Stock offered by any of these risks. As a result,this prospectus could decline, and you couldmay lose someall or allpart of your investmentinvestment. You should read the section entitled “Special Note Regarding Forward-Looking Statements” above for a discussion of what types of statements are forward-looking statements, as well as the significance of such statements in our common stock.the context of this prospectus. Additional risks and uncertainties that we do not presently know or that we currently knowndeem immaterial may also have a material adverse effect on our business.

DESCRIPTION OF THE TRANSACTIONS

Purchase Agreements

On February 15, 2022, we entered into the SPA with Wood River Capital, LLC, an affiliate of Koch Strategic Platforms (the “selling shareholder”) and a note purchase agreement (the “Note Purchase Agreement” and together with the SPA, the “Purchase Agreements”).

Pursuant to us or other factors not perceived by usthe terms of the SPA, we agreed to present significant riskssell to our businessthe selling shareholder an aggregate of 1,791,986 shares of Common Stock at this time also may impair our business operations.a purchase price equal to $27.902 per share, for aggregate gross proceeds of approximately $50.0 million (the “Common Stock Private Placement”). The Common Stock Private Placement closed on March 28, 2022.

CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENT

This prospectusPursuant to the terms of the Note Purchase Agreement, we agreed to sell to the selling shareholder $100,000,000 in aggregate principal amount of the Notes, convertible into shares of Common Stock (the “Convertible Note Private Placement”). The Convertible Note Private Placement closed on February 18, 2022 and the documentsNotes were issued on such date.

The Notes are governed by a form of indenture (the “Indenture”) incorporated by reference into the Notes. The Notes bear interest at the Secured Overnight Financing Rate (“SOFR”) plus 5.50% per annum if interest is paid in this prospectus include forward-looking statements withincash (“Cash Interest”), or, if interest is paid in kind (through an increase in the meaning of Section 27Aprincipal amount of the Securities Act and Section 21Eoutstanding Notes or through the issuance of additional Notes), at SOFR plus 6.50% per annum (“PIK Interest”). Under the terms of the Securities Exchange Actinvestment, SOFR has a floor of 1934, as amended,1% and a cap of 3%. We can elect to make any interest payment through Cash Interest, PIK Interest or any combination thereof. Interest on the Exchange Act,Notes is payable semi-annually in arrears on June 30 and December 30, commencing on June 30, 2022. It is expected that relatethe Notes will mature on February 18, 2027, subject to future eventsearlier conversion, redemption or our future financial performance and involve known and unknown risks, uncertainties and other factors that may cause our actual results, levels of activity, performance or achievements to differ materially from any future results, levels of activity, performance or achievements expressed or implied by these forward-looking statements. Words such as, but not limited to, “believe,” “expect,” “anticipate,” “estimate,” “intend,” “may,” “plan,” “potential,” “predict,” “project,” “targets,” “likely,” “will,” “would,” “could,” “should,” “continue,” and similar expressions or phrases, orrepurchase.

The Notes are convertible at the negative of those expressions or phrases, are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words. Although we believe that we have a reasonable basis for each forward-looking statement contained in this prospectus and incorporated by reference in this prospectus, we caution you that these statements are based on our projectionsoption of the future that are subjectholder at any time until the business day prior to known and unknown risks and uncertainties and other factors that may cause our actual results, level of activity, performance or achievements expressed or implied by these forward-looking statements, to differ. The sections in our periodic reports, including our Annual Report on Form 10-K for the fiscal year ended December 31, 2016, entitled “Business,” “Risk Factors,” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” as well as other sections in this prospectus and the documents or reports incorporated by reference in this prospectus, discuss some of the factors that could contribute to these differences. These forward-looking statements include, among other things, statements about:

We may not actually achieve the plans, intentions or expectations disclosed in our forward-looking statements, and you should not place undue reliance on our forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in the forward-looking statements we make. We have included important cautionary statements in this prospectus, particularly in the “Risk Factors” section and the risk factors incorporated by reference herein, that we believe could cause actual results or events to differ materially from the forward-looking statements that we make. Our forward-looking statements do not reflect the potential impact of any future acquisitions, mergers, dispositions, joint ventures or investments we may make.

You should read this prospectus, the documents and reports incorporated by reference in this prospectus, and the documents that we reference in this prospectus and have filed as exhibits to the registration statement of which this prospectus forms a part, completelyif there is no review by the U.S. Securities and withExchange Commission (the “SEC”), or within 120 days following the understanding that our actual future results may be materially different from what we expect. The forward-looking statements contained in this prospectus are made asfiling of the date of this prospectus and the forward-looking statements contained in any document or report incorporated by reference in this prospectus are made as of the dates of such documents or reports. We do not assume, and specifically disclaim, any obligation to update any forward-looking statements, whether as a result of new information, future events or otherwise.

USE OF PROCEEDS

We are filing the registration statement in the event of which this prospectus formssuch a partreview.

The Purchase Agreements contain customary representations, registration rights, warranties and agreements by us, customary conditions to permit holdersclosing, indemnification obligations by us, including for liabilities under the Securities Act, termination provisions, and other obligations and rights of the shares of our common stock describedparties. The representations, warranties and covenants contained in the section entitled “Selling Stockholders”Purchase Agreements were made only for purposes of such agreements and as of specific dates, were solely for the benefit of the parties to resell such shares. agreements, and may be subject to limitations agreed upon by the contracting parties.

USE OF PROCEEDS

We will not receive any proceeds from the resalesale of the Shares by the selling shareholder.

The selling shareholder will pay all underwriting discounts, selling commissions and expenses incurred by it for brokerage, accounting, tax or legal services or the services of any other advisor to the selling shareholder incurred by the selling shareholder in connection with the sale of the Shares, if any. We will bear all other costs, fees and expenses incurred in effecting the registration of the Shares covered by this prospectus, including, without limitation, all registration and filing fees, NYSE listing fees and fees and expenses of our counsel and our accountants.

SELLING SHAREHOLDER

The Shares being offered for resale by the selling shareholder pursuant to the Form S-3 of which this prospectus forms a part are the Shares issued to the selling shareholder pursuant to the Purchase Agreements. For additional information regarding the issuance of those Shares and our relationship with the selling shareholder, see “Description of the Transactions” above. We are registering the Shares in order to permit the selling shareholder to offer the Shares for resale from time to time.

The table below lists the selling shareholder and other information regarding the beneficial ownership of shares of Common Stock by the selling shareholder. The second column lists the number of shares of Common Stock beneficially owned by the selling shareholder. The third column lists the shares of Common Stock being offered by this prospectus by the selling stockholders.

SELLING STOCKHOLDERS

This prospectus coversshareholder. The fourth column lists the resaleshares of Common Stock held by the selling stockholders identified belowshareholder after completion of 6,620,452this offering. The fifth column lists the percentage ownership held by the selling shareholder after completion of this offering to the extent such percentage exceeds 1% of the total number of shares of Common Stock outstanding at that time. Pursuant to Rules 13d-3 and 13d-5 of the Exchange Act, beneficial ownership includes any shares of our common stock. These shares were issuedCommon Stock as to the selling stockholders by Aspen Aerogels, Inc. (“Aspen,” “we,” “us”which a stockholder has sole or the “Company”) principally upon conversion of theirshared voting power or investment power, and also any shares of convertible preferred stock and convertible promissory notes into common stockour Common Stock which the stockholder has the right to acquire within 60 days of April 30, 2022. The information presented regarding the selling shareholder is based, in connection with our initial public offering of common stockpart, on information the selling shareholder provided to us in June 2014 (the “IPO”) or were purchased by certain of those selling stockholderswriting specifically for use in the IPO.  In addition, certain of these shares were issued to members of our board of directors at the time of the IPOthis prospectus. Except as compensation for their service as directors and priordescribed below, to our filing of a registration statement on Form S-8 registering shares reserved for grant under our 2014 Employee, Director and Consultant Equity Incentive Plan.  We are registering the resale of the shares issued upon conversion of convertible preferred stock and convertible promissory notes as required by the Sixth Amended and Restated Registration Rights Agreement that we entered into with the investors named therein, dated as of June 11, 2012, as amended (the “Registration Rights Agreement”).  None of our selling stockholders received any of our securities as compensation for underwriting services. We will not receive any proceeds from the resale of the common stock byknowledge, the selling stockholders.

Except as disclosed in the footnotes below, none of the selling stockholdersshareholder has not been an officer or director of oursthe Company or any of our predecessorsaffiliates within the past three years or had any material relationship with us or our affiliates within the past three years. Except as disclosed in the footnotes below, no selling stockholder had a material relationship with the Company or any of its affiliates within the last three years. Except as disclosed in the footnotes below, none of the selling stockholdersOur knowledge is affiliated with a broker dealer.

The following table and the accompanying footnotes are based in part on information supplied to usprovided by the selling stockholders. shareholder questionnaire in connection with the filing of this prospectus, as well as information obtained from relevant Schedule 13D and 13G filings.

The tableinformation below assumes the offer and footnotes assume that the selling stockholders will sellsale of all of the shares listed. However, becauseShares registered hereby and assumes no further acquisitions or dispositions of Common Stock by the selling stockholdersshareholder. The selling shareholder may sell all, some or somenone of theirits shares underin this prospectus from time to time, or in another permitted manner, we cannot assure you asoffering. See “Plan of Distribution.”

In addition to the actual number of shares that will be sold by the selling stockholders or that will be held by the selling stockholders after completion of any sales. We do not know how long the selling stockholders will hold the shares before selling them.

Beneficialassumptions described above, beneficial ownership is determined in accordance with the rules and regulations of the SEC and generally includes voting or investment power with respect toover securities. To our common stock. Shares of our common stock subject to options, restricted stock units or warrants that are currently exercisable or exercisable within 60 days of November 1, 2017 are considered outstanding and beneficially owned byknowledge, unless otherwise indicated, the person holding the options, restricted stock units or warrants for the purpose of calculating the percentage ownership of that person but not for the purpose of calculating the percentage ownership of any other person. Except as otherwise notedentity named in the footnotestable below we believe the persons and entities in this table havehas sole voting and investinginvestment power with respect to allits shares of theCommon Stock. Percentage of beneficial ownership is based on 36,080,825 shares of our common stock beneficially owned by them, subject to community property laws, where applicable. The inclusionCommon Stock outstanding as of any shares in this table does not constitute an admission of beneficial ownership by the persons named below. The beneficial owners listed below are sorted alphabetically by name.April 30, 2022.

or other transactions with broker-dealers or other financial institutions or the creation of one or more derivative securities which require the delivery to such broker-dealer or other financial institution of shares offered by this prospectus, which shares such broker-dealer or other financial institution may resell pursuant to this prospectus (as supplemented or amended to reflect such transaction).

Broker-dealers engaged by the selling shareholder may arrange for other broker-dealers to participate in sales. If the selling shareholder effects certain transactions by selling shares of Common Stock to or through underwriters, broker-dealers or agents, such underwriters, broker-dealers or agents may receive commissions in the form of discounts, concessions or commissions from such selling shareholder or commissions from purchasers of the Common Stock for whom they may act as agent or to whom they may sell as principal. Such commissions will be in amounts to be negotiated, but, except as set forth in a supplement to this prospectus, in the case of an agency transaction will not be in excess of a customary brokerage commission in compliance with applicable rules of the Financial Industry Regulatory Authority (“FINRA”); and in the case of a principal transaction, a markup or markdown in compliance with applicable FINRA rules.

The aggregate proceeds to the selling stockholdersshareholder from the sale of the common stockCommon Stock offered by themit will be the purchase price of the common stockCommon Stock less discounts or commissions, if any. Each of theThe selling stockholdersshareholder reserves the right to accept and, together with their agentsits agent from time to time, to reject, in whole or in part, any proposed purchase of common stockCommon Stock to be made directly or through agents. We will not receive any of the proceeds from this offering.

The selling stockholdersshareholder also may resell all or a portion of the shares in open market transactions in reliance upon Rule 144 under the Securities Act, if available, or pursuant to other available exemptions from the registration requirements under the Securities Act, rather than this prospectus, provided that it meets the criteria and conform to the requirements of that rule. Registration of the Shares covered by this prospectus does not mean that any shares of the Common Stock will be offered or sold.

The selling shareholder may engage in at-the-market offerings and offer the Common Stock into an existing trading market in accordance with Rule 415(a)(4) under the Securities Act on the terms described in the prospectus supplement relating thereto. Underwriters, dealers and agents who participate in any at-the-market-offerings will be described in the prospectus supplement relating thereto.

The selling shareholder and any underwriters, broker-dealers or agents that participate in the sale of the common stockCommon Stock or interests therein may be “underwriters” within the meaning of Section 2(a)(11)2(11) of the Securities Act. Any discounts, commissions, concessions or profit they earnit earns on any resale of the shares may be underwriting discounts and commissions under the Securities Act. Selling stockholders who are “underwriters”If the selling shareholder is an “underwriter” within the meaning of Section 2(a)(11)2(11) of the Securities Act, it will be subject to the prospectus delivery requirements of the Securities Act.

To the extent required, the shares of our common stockCommon Stock to be sold, the namesname of the selling stockholders,shareholder, the respective purchase prices and public offering prices, the names of any agents, dealer or underwriter, and any applicable commissions or discounts with respect to a particular offer will be set forth in an accompanying prospectus supplement or, if appropriate, a post-effective amendment to the registration statement that includes this prospectus.

In order to comply with the securities laws of some states, if applicable, the common stockCommon Stock may be sold in these jurisdictions only through registered or licensed brokers or dealers. In addition, in some states the common stockCommon Stock may not be sold unless it has been registered or qualified for sale or an exemption from registration or qualification requirements is available and is complied with.

If at the time of any offering made under this prospectus, a member of FINRA participating in the offering has a “conflict of interest” as defined in FINRA Rule 5121 (“Rule 5121”), that offering will be conducted in accordance with the relevant provisions of Rule 5121.

We have advised the selling stockholdersshareholder that the anti-manipulation rules of Regulation M promulgated under the Exchange Act may apply to sales of shares in the market and to the activities of the selling stockholdersshareholder and theirits affiliates. In addition, to the extent applicable we will make copies of this prospectus (as it may be supplemented or amended from time to time) available to the selling stockholdersshareholder for the purpose of satisfying the prospectus delivery requirements of the Securities Act. The selling stockholdersshareholder may indemnify any broker-dealer that participates in transactions involving the sale of the shares against certain liabilities, including liabilities arising under the Securities Act.

To the extent required by the Registration Rights Agreement, weWe have agreed to indemnify certain of the selling stockholdersshareholder against liabilities, including liabilities under the Securities Act and state securities laws, relating to the registration of certain of the sharesShares offered by this prospectus.

We expecthave agreed with the selling shareholder to use our commercially reasonable efforts to keep the registration statement of which this prospectus constitutes a part effective for a period of at least eighteen months afteruntil the date the registration statement is declared effective by the SEC or, if earlier, untilon which all of the shares covered by this prospectus have been disposed of pursuant to andincluded in accordance with the registration statement.

DESCRIPTION OF CAPITAL STOCK

The following statements are qualified in their entirety by reference to the detailed provisions of our restated certificate of incorporation and restated bylaws.

Authorized Capitalizationstatement have actually been sold.

We currently have authorized capital stock of 125,000,000 shares of our common stock, par value $0.00001 per share, and 5,000,000 shares of preferred stock, par value $0.00001 per share.

As of November 1, 2017, we have 23,637,115 shares of common stock outstanding held of record by 41 stockholders and no shares of preferred stock outstanding.

Common Stock

Holders of our common stock are entitled to one vote for each share held of record on all matters submitted to a vote of the stockholders, and do not have cumulative voting rights. Subject to preferences that may be applicable to any outstanding shares of preferred stock, holders of common stock are entitled to receive ratably such dividends, if any, as may be declared from time to time by our board of directors out of funds legally available for dividend payments. All outstanding shares of common stock are fully paid and nonassessable. The holders of common stock have no preferences or rights of conversion, exchange, pre-emption or other subscription rights. There are no redemption or sinking fund provisions applicable to the common stock. In the event of any liquidation, dissolution or winding-up of our affairs, holders of common stock will be entitled to share ratably in our assets that are remaining after payment or provision for payment of all of our debts and obligations and after liquidation payments to holders of outstanding shares of preferred stock, if any.

Preferred Stock

If we issue preferred stock in the future, such preferred stock would have priority over common stock with respect to dividends and other distributions, including the distribution of assets upon liquidation.  Our board of directors has the authority, without further stockholder authorization, to issue from time to time up to 5,000,000 shares of preferred stock in one or more series and to fix the terms, limitations, voting rights, relative rights and preferences and variations of each series. Although we have no present plans to issue any shares of preferred stock, the issuance of shares of preferred stock, or the issuance of rights to purchase such shares, could decrease the amount of earnings and assets available for distribution to the holders of common stock, could adversely affect the rights and powers, including voting rights, of the common stock and could have the effect of delaying, deterring or preventing a change of control of us or an unsolicited acquisition proposal.

Warrants

As of November 1, 2017, we had outstanding warrants to purchase 120 shares of our common stock at an exercise price of $8.25 per share, which expire on December 29, 2017.

Registration Rights

Pursuant to our registration rights agreement to which certain of our principal stockholders, directors and executive officers are parties, including GKFF Ventures I, LLC; Reservoir Capital Partners, L.P. and affiliated funds; certain entities affiliated with Fidelity Investments; Donald R. Young, our President, Chief Executive Officer and one of our directors; and John F. Fairbanks, our Vice President, Chief Financial Officer and Treasurer, are entitled to registration rights with respect to the shares of common stock held by them. These shares include substantially all of the shares held by GKFF Ventures I, LLC; Reservoir Capital Partners, L.P. and affiliated funds; certain entities affiliated with Fidelity Investments; and certain shares held by Donald R. Young, our President, Chief Executive Officer and one of our directors; and John F. Fairbanks, our Vice President, Chief Financial Officer and Treasurer. We are generally required to pay all expenses incurred in connection with registrations effected in connection with the following rights, excluding underwriting discounts. All registration rights described below will terminate at the earlier of (1) the seventh anniversary of the completionregistration of our initial public offering, or June 18, 2021, (2) such shares have been registered under the Securities Act, such registration statement has been declared

effective and the shares have been disposed of pursuant to such effective registration statement, and (3) with respect to any holder of registrable shares that (together with its affiliates) holds less than 1% of our common stock (on an as-if-converted to common stock basis), when such holder can sell all of such shares without limitation under Rule 144 promulgated under the Securities Act during any 90 day period. The registration statement of which this prospectus forms a part is a shelf registration statement that we are required to file under the registration rights agreementShares pursuant to the “ – Form S-3 rights” section below.Purchase Agreements, including, without limitation, SEC filing fees and expenses of compliance with state securities or “blue sky” laws; provided, however, that a selling shareholder will pay all underwriting discounts and selling commissions, if any.

Piggyback rights. If we propose to register any of our equity securities under the Securities Act, other than in connection with (i) a registration relating solely to our employee benefit plans, or (ii) a registration relating solely to a business combination or merger involving us, the holders of these registrable shares are entitled to notice of such registration and are entitled to include their shares of common stock in the registration. Under certain circumstances, the underwriters, if any, may limit the number of shares included in any such registration.

Form S-3 rights. If we become eligible to file registration statements on Form S-3, subject to specified limitations, the holders of these registrable shares may require us to register all or a portion of their registrable shares on Form S-3, if the anticipated aggregate offering price of such securities is at least $2,000,000. Such requests for registration will not be considered a demand registration pursuant to the “— Demand rights” section above. We are not required to (i) effect more than two such registrations in any 12-month period or (ii) keep effective at any one time more than one registration statement on Form S-3 with respect to the registrable shares. Stockholders with these registration rights who are not part of an initial registration demand are entitled to notice and are entitled to include their shares of common stock in the registration. Under certain circumstances, the underwriters, if any, may limit the number of shares included in any such registration.

Anti-Takeover Effects of Delaware Law and Our Restated Certificate of Incorporation and Restated By-Laws

The provisions of Delaware law, our restated certificate of incorporation and our restated by-laws discussed below could discourage or make it more difficult to accomplish a proxy contest or other change in our management or the acquisition of control by a holder of a substantial amount of our voting stock. It is possible that these provisions could make it more difficult to accomplish, or could deter, transactions that stockholders may otherwise consider to be in their best interests or in our best interests. These provisions are intended to enhance the likelihood of continuity and stability in the composition of our board of directors and in the policies formulated by the board of directors and to discourage certain types of transactions that may involve an actual or threatened change of our control. These provisions are designed to reduce our vulnerability to an unsolicited acquisition proposal and to discourage certain tactics that may be used in proxy fights. Such provisions also may have the effect of preventing changes in our management.

Delaware Statutory Business Combinations Provision

We are subject to the anti-takeover provisions of Section 203 of the Delaware General Corporation Law. Section 203 prohibits a publicly-held Delaware corporation from engaging in a “business combination” with an “interested stockholder” for a period of three years after the date of the transaction in which the person became an interested stockholder, unless the business combination is, or the transaction in which the person became an interested stockholder was, approved in a prescribed manner or another prescribed exception applies. For purposes of Section 203, a “business combination” is defined broadly to include a merger, asset sale or other transaction resulting in a financial benefit to the interested stockholder, and, subject to certain exceptions, an “interested stockholder” is a person who, together with his or her affiliates and associates, owns, or within three years prior, did own, 15% or more of the corporation’s voting stock.

Classified Board of Directors; Removal of Directors for Cause

Our restated certificate of incorporation and restated by-laws provide that our board of directors are divided into three classes, with the term of office of the first class to expire at the first annual meeting of stockholders following the initial classification of directors, the term of office of the second class to expire at the second annual meeting of stockholders following the initial classification of directors and the term of office of the third class to expire at the third annual meeting of stockholders following the initial classification of directors. At each annual meeting of stockholders, directors elected to succeed those directors whose terms expire will be elected for a three-year term of office. All directors elected to our classified board of directors will serve until the election and qualification of their respective successors or their earlier resignation or removal. The board of directors is authorized to create new directorships and to fill such positions so created and is permitted to specify the class to which any such new position is assigned. The person filling such position would serve for the term applicable to that class. The board of directors, or its remaining members, even if less than a quorum, is also empowered to fill vacancies on the board of directors occurring for any reason for the remainder of the term of the class of directors in which the vacancy occurred. Members of the board of directors may only be removed for cause and only by the affirmative vote of 75% of our outstanding voting stock. These provisions are likely to increase the time required for stockholders to change the composition of the board of directors. For example, at least two annual meetings will be necessary for stockholders to effect a change in a majority of the members of the board of directors.

Advance Notice Provisions for Stockholder Proposals and Stockholder Nominations of Directors

Our restated by-laws provide that, for nominations to the board of directors or for other business to be properly brought by a stockholder before a meeting of stockholders, the stockholder must first have given timely notice of the proposal in writing to our Secretary. For an annual meeting, a stockholder’s notice generally must be delivered not less than 90 days nor more than 120 days prior to the anniversary of the previous year’s annual meeting. For a special meeting, the notice must generally be delivered not earlier than the 90th day prior to the meeting and not later than the later of (1) the 60th day prior to the meeting or (2) the 10th day following the day on which public announcement of the meeting is first made. Detailed requirements as to the form of the notice and information required in the notice are specified in the restated by-laws. If it is determined that business was not properly brought before a meeting in accordance with our bylaw provisions, such business will not be conducted at the meeting.

Special Meetings of Stockholders

Special meetings of the stockholders may be called only by our board of directors pursuant to a resolution adopted by a majority of the total number of directors.

No Stockholder Action by Written Consent

Any action to be effected by our stockholders must be effected at a duly called annual or special meeting of the stockholders.

Super Majority Stockholder Vote Required for Certain Actions

The Delaware General Corporation Law provides generally that the affirmative vote of a majority of the shares entitled to vote on any matter is required to amend a corporation’s certificate of incorporation or by-laws, unless the corporation’s certificate of incorporation or by-laws, as the case may be, requires a greater percentage. Our restated certificate of incorporation requires the affirmative vote of the holders of at least 75% of our outstanding voting stock to amend or repeal any of the provisions discussed in this section of this prospectus entitled “— Anti-Takeover Effects of Delaware Law and Our Restated Certificate of Incorporation and Restated By-Laws” or to reduce the number of authorized shares of common stock or preferred stock. This 75% stockholder vote would be in addition to any separate class vote that might in the future be required pursuant to the terms of any preferred stock that might then be outstanding. In addition, a 75% vote is also required for any amendment to, or repeal of, our restated by-laws by the stockholders. Our restated by-laws may be amended or repealed by a simple majority vote of the board of directors.

Exclusive Forum

Our restated certificate of incorporation provides that, subject to limited exceptions, a state or federal court located within the State of Delaware will be the sole and exclusive forum for (1) any derivative action or proceeding brought on our behalf, (2) any action asserting a claim of breach of a fiduciary duty owed by any of our directors, officers or other employees to us or our stockholders, (3) any action asserting a claim against us arising pursuant to any provision of the Delaware General Corporation Law, our certificate of incorporation or our by-laws, or (4) any other action asserting a claim against us that is governed by the internal affairs doctrine. Any person or entity purchasing or otherwise acquiring any interest in shares of our capital stock shall be deemed to have notice of and to have consented to the provisions of our restated certificate of incorporation described above. Although we believe these provisions benefit us by providing increased consistency in the application of Delaware law for the specified types of actions and proceedings, the provisions may have the effect of discouraging lawsuits against our directors and officers. The enforceability of similar choice of forum provisions in other companies’ certificates of incorporation has been challenged in legal proceedings, and it is possible that, in connection with one or more actions or proceedings described above, a court could find the choice of forum provisions contained in our restated certificate of incorporation to be inapplicable or unenforceable.

Limitation of Directors’ and Officers’ Liability and Indemnification

The Delaware General Corporation Law authorizes corporations to limit or eliminate, subject to specified conditions, the personal liability of directors to corporations and their stockholders for monetary damages for breach of their fiduciary duties. Our existing restated certificate of incorporation, as amended, limits the liability of our directors to the fullest extent permitted by Delaware law.

We have obtained director and officer liability insurance to cover liabilities our directors and officers may incur in connection with their services to us. Our restated certificate of incorporation and restated by-laws also provide that we will indemnify and advance expenses to any of our directors and officers who, by reason of the fact that he or she is one of our officers or directors, is involved in a legal proceeding of any nature. We will repay certain expenses incurred by a director or officer in connection with any civil, criminal, administrative or investigative action or proceeding, including actions by us or in our name. Such indemnifiable expenses include, to the maximum extent permitted by law, attorney’s fees, judgments, fines, ERISA excise taxes, penalties, settlement amounts and other expenses reasonably incurred in connection with legal proceedings. A director or officer will not receive indemnification if he or she is found not to have acted in good faith and in a manner he or she reasonably believed to be in, or not opposed to, our best interest.

We have entered into indemnification agreements with each of our non-employee directors and certain officers. These agreements provide that we will, among other things, indemnify and advance expenses to our directors and officers for certain expenses, including attorneys’ fees, judgments, fines and settlement amounts incurred by any such person in any investigation, action or proceeding, including any action by us arising out of such person’s services as our director or officer, or any other company or enterprise to which the person provides services at our request. We believe that these provisions and agreements are necessary to attract and retain qualified persons as directors and officers.

Such limitation of liability and indemnification does not affect the availability of equitable remedies. In addition, we have been advised that in the opinion of the SEC, indemnification for liabilities arising under the Securities Act is against public policy as expressed in the Securities Act and is therefore unenforceable.

There is no pending litigation or proceeding involving any of our directors, officers, employees or agents in which indemnification will be required or permitted. We are not aware of any threatened litigation or proceeding that may result in a claim for such indemnification.

Transfer Agent and Registrar

The transfer agent and registrar for our common stock is Computershare Trust Company, N.A., with offices at 250 Royall Street, Canton, Massachusetts 02021.

LEGAL MATTERS

The validity of the shares of common stock being offered by this prospectusShares registered hereunder has been passed upon for us by Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C., Boston, Massachusetts.

EXPERTS

The consolidated financial statements and schedule of Aspen Aerogels, Inc. as of December 31, 20162021 and 2015,2020 and for each of the years in the three-year period ended December 31, 2016,2021, and management’s assessment of the effectiveness of internal control over financial reporting as of December 31, 2021 have been incorporated by reference herein and in the registration statement in reliance upon the reportsreport of KPMG LLP, independent registered public accounting firm, incorporated by reference herein, and upon the authority of said firm as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

We are subjectAs permitted by SEC rules, this prospectus, which constitutes a part of a registration statement on Form S-3 that we have filed with the SEC, omits certain of the information set forth in the registration statement. Accordingly, you should refer to the registration statement and its exhibits for further information requirementswith respect to us and our Common Stock. Copies of the Exchange Act,registration statement and its exhibits are requiredon file at the offices of the SEC. This prospectus contains statements concerning documents filed as exhibits. For the complete text of any of these documents, we refer you to the copy of the document filed as an exhibit to the registration statement.

We file annual, quarterly and current reports, proxy statements,and information statements and other information with the SEC. You may readThe SEC also maintains an Internet site that contains reports, proxy and copy this information for a copying fee, atstatements, and other information regarding issuers that file electronically with the SEC’s Public Reference Room at 100 F Street, N.E., Washington, D.C. 20549 on official business days during the hoursSEC. The address of 10:00 a.m. to 3:00 p.m. Please call the SEC at 1-800-SEC-0330 for more information on its Public Reference Room. Our SEC filings are also available to the public from commercial document retrieval services, and at the website maintained by the SEC at http://www.sec.gov.that site is www.sec.gov.

We also maintain a website at http://www.aerogel.com with information about our company and through which you canmay access ourthese materials and other filings with the SEC free of charge as soon as reasonably practicable after they are filed electronically with, or furnished to, the SEC. InformationExcept for the documents incorporated by reference as described below under “Incorporation of Certain Documents by Reference”, information contained on or accessible from our website or any other website is not incorporated into this prospectus and does not constitute a part of this prospectus. We have included ourOur website address in this prospectus solely asreferenced above is intended to be an inactive textual reference.reference only and not an active hyperlink to our website.

INFORMATION INCORPORATEDINCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

The SEC allows us to “incorporate by reference” into this prospectus the information that we have filedfile with the SEC. ThisSEC, which means that we can disclose important information to you by referring you to other documents that contain that information.filed separately with the SEC. The information incorporated by reference is considered part of this prospectus.prospectus, and any information that we file with the SEC subsequent to this prospectus and prior to the termination of the offering referred to in this prospectus will automatically be deemed to update and supersede this information. We incorporate by reference into this prospectus the documents listed below:below (excluding any portions of such documents that have been “furnished” but not “filed” for purposes of the Exchange Act unless specifically incorporated by reference herein or therein):

AnyWe also incorporate by reference all documents we subsequently file with the SEC (other than information furnished pursuant to Item 2.02 or Item 7.01 of Form 8-K or as otherwise permitted by SEC rules) pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act after the initial filing of the registration statement contained inof which this prospectus is a part (including prior to the effectiveness of the registration statement) and prior to the termination of the offering.

This prospectus is part of a registration statement on Form S-3 that we have filed with the SEC relating to the securities. As permitted by SEC rules, this prospectus does not contain all of the information included in the registration statement and the accompanying exhibits and schedules we file with the SEC. We have filed certain legal documents that control the terms of the Common Stock offered by this prospectus as exhibits to the registration statement. We may file certain other legal documents that control the terms of the Common Stock offered by this prospectus as exhibits to reports we file with the SEC. You may refer to the registration statement and the exhibits and schedules for more information about us and our securities. The registration statement and exhibits and schedules are also available through the SEC’s website at www.sec.gov.

We will provide, without charge and upon oral or inwritten request, to each person, including any beneficial owner, to whom a document incorporated or deemedcopy of this prospectus has been delivered, a copy of any of the documents referred to beabove as being incorporated by reference into this prospectus will be deemed to be modified or superseded for purposes of this prospectus to the extent that a statement contained in this prospectus or any other subsequently filed document that is deemed to be incorporated by reference into this prospectus modifies or supersedes the statement. Any statements so modified or superseded shallbut not be deemed, except as so modified or superseded, to constitute a part of this prospectus.

delivered with it. You may requestobtain a copy of these documents, orally or in writing, which will be provided to youfilings, at no cost, by contacting:

writing or calling us at Aspen Aerogels, Inc.

, Attn: Investor Relations, 30 Forbes Road, Building B, Northborough, MA 01532, (508) 691-1111. Exhibits to the filings will not be provided, however, unless those exhibits have been specifically incorporated by reference in this prospectus.

Attention: Investor Relations

Telephone: (508) 691-1111

You may also access these documents on our website, http://www.aerogel.com.

PART II

II. INFORMATION NOT REQUIRED IN PROSPECTUS

The following table sets forth the fees and expenses incurred and to be incurred in connection with the registrationsale of the securities being registered hereby, all of which will be borne by us. Except forthe registrant. Other than the SEC registration fee, allthe amounts stated are estimates.

and settlement amounts incurred by any such person in any investigation, action or proceeding, including any action by us arising out of such person’s services as our director, or any other company or enterprise to which the future.person provides services at our request. We believe that these provisions and agreements are necessary to attract and retain qualified persons as directors and officers.

Insurance Policies. We have purchasedobtained director and intendofficer liability insurance to maintain insurance on behalf of any person who is or was a director or officer against any loss arising from any claim asserted against him or hercover liabilities our directors and incurred by him or herofficers may incur in any such capacity, subjectconnection with their services to certain exclusions.us.

The foregoing discussion of our restated certificate of incorporation, restated by-laws,bylaws, indemnification agreements, indemnity agreement, and Delaware law is not intended to be exhaustive and is qualified in its entirety by such restated certificate of incorporation, restated by-laws,bylaws, indemnification agreements, indemnity agreement, or law.

Reference is made to our undertakings in Item 17 with respect to liabilities arising under the Securities Act.

EXHIBIT INDEXThe exhibits to this registration statement are listed in the Exhibit Index to this registration statement, which immediately precedes the Signature Page and which Exhibit Index is hereby incorporated by reference.

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(a) The undersigned registrant hereby undertakes:

(1) To file, during any period in which offers or sales are being made, a post-effective amendment to this registration statement:

(i) To include any prospectus required by Sectionsection 10(a)(3) of the Securities Act of 1933;

(ii) To reflect in the prospectus any facts or events arising after the effective date of the registration statement (or the most recent post-effective amendment thereof) which, individually or in the aggregate, represent a fundamental change in the information set forth in the registration statement. Notwithstanding the foregoing, any increase or decrease in volume of securities offered (if the total dollar value of securities offered would not exceed that which was registered) and any deviation from the low or high end of the estimated maximum offering range may be reflected in the form of prospectus filed with the Commission pursuant to Rule 424(b) if, in the aggregate, the changes in volume and price represent no more than 20 percenta 20% change in the maximum aggregate offering price set forth in the “Calculation of Registration Fee” table in the effective registration statement; and

(iii) To include any material information with respect to the plan of distribution not previously disclosed in the registration statement or any material change to such information in the registration statement.statement;

Provided,provided, however that: Paragraphs, that paragraphs (a)(1)(i), (a)(1)(ii) and (a)(1)(iii) of this section do not apply if the information required to be included in a post-effective amendment by those paragraphs is contained in reports filed with or furnished to the Commission by the registrant pursuant to section 13 or section 15(d) of the Securities Exchange Act of 1934 that are incorporated by reference in the registration statement, or is contained in a form of prospectus filed pursuant to Rule 424(b) that is part of the registration statement.

(2) That, for the purpose of determining any liability under the Securities Act of 1933, each such post-effective amendment shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(3) To remove from registration by means of a post-effective amendment any of the securities being registered which remain unsold at the termination of the offering.

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(4) That, for the purpose of determining liability under the Securities Act of 1933 to any purchaser:

(i) Each prospectus filed by the Registrantregistrant pursuant to Rule 424(b)(3) shall be deemed to be part of the registration statement as of the date the filed prospectus was deemed part of and included in the registration statement; and

(ii) Each prospectus required to be filed pursuant to Rule 424(b)(2), (b)(5), or (b)(7) as part of a registration statement in reliance on Rule 430B relating to an offering made pursuant to Rule 415(a)(1)(i), (vii), or (x) for the purpose of providing the information required by Sectionsection 10(a) of the Securities Act of 1933 shall be deemed to be part of and included in the registration statement as of the earlier of the date such form of prospectus is first used after effectiveness or the date of the first contract of sale of securities in the offering described in the prospectus. As provided in Rule 430B, for liability purposes of the issuer and any person that is at that date an underwriter, such date shall be deemed to be a new effective date of the registration statement relating to the securities in the registration statement to which that prospectus relates, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof; provided,thereof. Provided, however, that no statement made in a registration statement or prospectus that is part of the registration statement or made in a document incorporated or deemed incorporated by reference into the registration statement or prospectus that is part of the registration statement will, as to a purchaser with a time of contract of sale prior to such

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effective date, supersede or modify any statement that was made in the registration statement or prospectus that was part of the registration statement or made in any such document immediately prior to such effective date.

(5) That, for the purpose of determining liability of the registrant under the Securities Act of 1933 to any purchaser in the initial distribution of the securities, in a primary offering of securities of the undersigned registrant pursuant to this registration statement, regardless of the underwriting method used to sell the securities to the purchaser, if the securities are offered or sold to such purchaser by means of any of the following communications, the undersigned registrant will be a seller to the purchaser and will be considered to offer or sell such securities to such purchaser:

(i) Any preliminary prospectus or prospectus of the undersigned registrant relating to the offering required to be filed pursuant to Rule 424;

(ii) Any free writing prospectus relating to the offering prepared by or on behalf of the undersigned registrant or used or referred to by the undersigned registrant;

(iii) The portion of any other free writing prospectus relating to the offering containing material information about the undersigned registrant or its securities provided by or on behalf of the undersigned registrant; and

(iv) Any other communication that is an offer in the offering made by the undersigned registrant to the purchaser.

(b) That, for purposes of determining any liability under the Securities Act:

(1) The information omitted from the form of prospectus filed as part of the registration statement in reliance upon Rule 430A and contained in the form of prospectus filed by the registrant pursuant to Rule 424(b)(1) or (4) or 497(h) under the Securities Act shall be deemed to be part of the registration statement as of the time it was declared effective; and

(2) Each post-effective amendment that contains a form of prospectus shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(c) The undersigned registrant hereby undertakes that, for purposes of determining any liability under the Securities Act of 1933, each filing of the registrant’s annual report pursuant to section 13(a) or section 15(d) of

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the Securities Exchange Act of 1934 (and, where applicable, each filing of an employee benefit plan’s annual report pursuant to section 15(d) of the Securities Exchange Act of 1934) that is incorporated by reference in the registration statement shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(c)(d) Insofar as indemnification for liabilities arising under the Securities Act of 1933 may be permitted to directors, officers and controlling persons of the registrant, pursuant to the foregoing provisions, or otherwise, the registrant has been advised that in the opinion of the SECSecurities and Exchange Commission such indemnification is against public policy as expressed in the Act and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the registrant of expenses incurred or paid by a director, officer or controlling person of the registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Act and will be governed by the final adjudication of such issue.

(e) The undersigned registrant hereby undertakes to file an application for the purpose of determining the eligibility of the trustee to act under subsection (a) of Section 310 of the Trust Indenture Act (“Act”) in accordance with the rules and regulations prescribed by the Commission under section 305(b)(2) of the Act.

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EXHIBIT INDEX

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SIGNATURESSIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the Registrantregistrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the Towncity of Northborough, Commonwealth of Massachusetts, on November 7, 2017.May 4, 2022.

SIGNATURES AND POWER OF ATTORNEY

We, the undersigned officers and directors of Aspen Aerogels, Inc., hereby severally constitute and appoint Donald R. Young, and John F. Fairbanks, and each of them singly (with full power to each of them to act alone), our true and lawful attorneys-in-fact and agents, with full power of substitution and resubstitution in each of them foror him and in his name, place and stead, and in any and all capacities, to sign any and all amendments (including post-effective amendments) to this registration statement (or any other registration statement for the same offering that is to be effective upon filing pursuant to Rule 462(b) under the Securities Act of 1933), and to file the same, with all exhibits thereto and other documents in connection therewith, with the Securities and Exchange Commission, granting unto said attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done in and about the premises, as full to all intents and purposes as she or he might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them or their or her or his substitute or substitutes may lawfully do or cause to be done by virtue hereof.

Pursuant to the requirements of the Securities Act of 1933, this registration statement has been signed below by the following persons in the capacities and on the dates indicated.