Exhibit 5.1



                                        August 9, 2004

Ply Gem Industries, Inc.
303 West Major Street
Kearney, Missouri  64060

                       Registration Statement on Form S-4
                          (Registration No. 333-114041)

Ladies and Gentlemen:

      In connection with the Registration Statement on Form S-4, as amended (the
"Registration Statement") of Ply Gem Industries, Inc., a Delaware corporation
(the "Company"), and Ply Gem Holdings, Inc., a Delaware corporation
("Holdings"), Great Lakes Window, Inc., an Ohio corporation ("Great Lakes"),
Kroy Building Products, Inc., a Delaware corporation ("Kroy"), Napco, Inc., a
Delaware corporation ("Napco"), Napco Window Systems, Inc., a Delaware
corporation ("NWS"), Thermal-Gard, Inc., a




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Pennsylvania corporation ("Thermal Gard"), and Variform, Inc., a Missouri
corporation ("Variform") (collectively, the "Guarantors"), filed with the
Securities and Exchange Commission pursuant to the Securities Act of 1933, as
amended (the "Act"), and the rules and regulations thereunder (the "Rules"), you
have asked us to furnish our opinion as to the legality of the securities being
registered under the Registration Statement. The Registration Statement relates
to the registration under the Act of the Company's $225,000,000 aggregate
principal amount of 9% Senior Subordinated Notes due 2012 (the "Exchange Notes")
and the guarantees of the Exchange Notes by the Guarantors (the "Guarantees").

      The Exchange Notes are to be offered in exchange for the Company's
outstanding $225,000,000 aggregate principal amount of 9% Senior Subordinated
Notes due 2012 (the "Initial Notes") issued and sold by the Company on February
12, 2004 in an offering exempt from registration under the Act. The Exchange
Notes will be issued by the Company in accordance with the terms of the
Indenture (the "Indenture"), dated as of February 12, 2004, among the Company,
the Guarantors and U.S. Bank National Association, as trustee.

      In connection with the furnishing of this opinion, we have examined
originals or copies certified or otherwise identified to our satisfaction, of
the following documents (collectively, the "Documents"):

      1. the Registration Statement;

      2. the Indenture, including as exhibits thereto the form of Exchange Note
and the related Guarantees, included as Exhibit 4.1 to the Registration
Statement; and




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      3. the Registration Rights Agreement, dated as of February 12, 2004 (the
"Registration Rights Agreement), among the Company, the Guarantors and the
initial purchasers named therein, included as Exhibit 4.3 to the Registration
Statement.

      In addition, we have examined (i) such corporate records of the Company
and each Guarantor organized in the State of Delaware that we have considered
appropriate, including a copy of the certificate of incorporation, as amended,
and by-laws, as amended, of the Company and each Guarantor organized in the
State of Delaware, certified as in effect on the date of this letter, and copies
of resolutions of the board of directors of the Company and such Guarantors
relating to the issuance of the Exchange Notes and the Guarantees, certified by
officers of the Company and such Guarantors and (ii) those other certificates,
agreements and documents that we deemed relevant and necessary as a basis for
our opinion. We have also relied upon the factual matters contained in the
representations and warranties of the Company and the Guarantors made in the
Documents and upon certificates of public officials and the officers of the
Company and the Guarantors.

      In our examination of the documents referred to above, we have assumed,
without independent investigation, the genuineness of all signatures, the legal
capacity of all individuals who have executed any of the documents reviewed by
us, the authenticity of all documents submitted to us as originals, the
conformity to the originals of all documents submitted to us as certified,
photostatic, reproduced or conformed copies of valid existing agreements or
other documents, the authenticity of all the latter documents and that the
statements regarding matters of fact in the certificates, records, agreements,
instruments and documents that we have examined are accurate and complete. We
have






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also assumed, without independent investigation, (i) that the Exchange Notes and
Guarantees will be issued as described in the Registration Statement and (ii)
that the Exchange Notes and Guarantees will be in substantially the form
attached to the Indenture and that any information omitted from such form will
be properly added. With regards to certain matters of state law, we have relied,
with the Company's permission, upon the opinions of Lathrop & Gage L.C.,
Marshall & Melhorn LLC, and Saul Ewing LP, filed as Exhibits 5.2, 5.3 and 5.4,
respectively, to the Registration Statement.

      Based upon the above, and subject to the stated assumptions, exceptions
and qualifications, we are of the opinion that:

      1. When duly issued, authenticated and delivered against the surrender and
cancellation of the Initial Notes as set forth in the Registration Statement and
in accordance with the terms of the Indenture and Registration Rights Agreement,
the Exchange Notes will be legal, valid and binding obligations of the Company
enforceable against the Company in accordance with their terms, except that the
enforceability of the Exchange Notes may be subject to bankruptcy, insolvency,
reorganization, fraudulent conveyance or transfer, moratorium or similar laws
affecting creditors' rights generally and subject to general principles of
equity (regardless of whether enforceability is considered in a proceeding in
equity or at law).

      2. When duly executed, issued, and delivered against the surrender and
cancellation of the Initial Notes as set forth in the Registration Statement and
in accordance with the terms of the Indenture and Registration Rights Agreement,
the Guarantees will be legal, valid and binding obligations of each of the
Guarantors enforceable against each of the Guarantors in accordance with their
terms, except that enforceability of the





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Guarantees may be subject to bankruptcy, insolvency, reorganization, fraudulent
conveyance or transfer, moratorium or similar laws affecting creditors' rights
generally and subject to general principles of equity (regardless of whether
enforcement is considered in a proceeding in equity or at law).

      The opinions expressed above are limited to the laws of the State of New
York and the General Corporation Law of the State of Delaware. Our opinion is
rendered only with respect to the laws, and the rules, regulations and orders
under those laws that are in effect on the effective date of the Registration
Statement.

      We hereby consent to use of this opinion as an exhibit to the Registration
Statement and to the use of our name under the heading "Legal Matters" contained
in the Prospectus included in the Registration Statement. In giving this
consent, we do not thereby admit that we come within the category of persons
whose consent is required by the Act or the Rules.


                                  Very truly yours,



                  /s/ PAUL, WEISS, RIFKIND, WHARTON & GARRISON LLP

                      PAUL, WEISS, RIFKIND, WHARTON & GARRISON LLP