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                                                                    Exhibit 3.21
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                          CERTIFICATE OF INCORPORATION

                                       OF

                    WIND GAP REAL PROPERTY ACQUISITION CORP.
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                THE UNDERSIGNED, being a natural person for the purposes of
organizing a corporation under the General Corporation Law of the State of
Delaware, hereby certifies that:

                FIRST: The name of the Corporation is Wind Gap Real Property
Acquisition Corp.

                SECOND: The address of the registered office of the Corporation
in the State of Delaware is 32 Loockerman Square, Suite L-100, City of Dover,
County of Kent, State of Delaware. The name of the registered agent of the
Corporation in the State of Delaware at such address is The Prentice-Hall
Corporation System, Inc.

                THIRD: The purpose of the Corporation is to engage in any lawful
act or activity for which corporations may be organized under the General
Corporation Law of the State of Delaware, as from time to time amended.

                FOURTH: The total number of shares of capital stock which the
Corporation shall have authority to issue is 1000, all of which shares shall be
Common Stock having a par value of $.001.

                FIFTH: The name and mailing address of the incorporator is
Shelley A. Sorkin, c/o ISP Management Company, Inc., 1361 Alps Road, Wayne, New
Jersey 07470.

                SIXTH: In furtherance and not in limitation of the powers
conferred by law, subject to any limitations contained elsewhere in these
articles of incorporation, By-laws of the Corporation may be adopted, amended or
repealed by a majority of the board of directors of the Corporation, but any
By-laws adopted by the board of directors may be amended or repealed by the
stockholders entitled to vote thereon. Election of directors need not be by
written ballot.

                SEVENTH: (a) A director of the Corporation shall not be
personally liable either to the Corporation or to any stockholder for monetary
damages for breach of fiduciary duty as a director, except (i) for any breach of
the director's duty of loyalty to the Corporation or its stockholders, or (ii)
for acts or omissions which are not in good faith or which involve intentional
misconduct or knowing violation of the law, or (iii) for any matter in respect
of which such director shall be liable under Section 174 of Title 8 of the
General Corporation Law of the State of Delaware or any amendment thereto or
successor provision thereto, or (iv) for any transaction from which the director
shall have derived an improper personal benefit. Neither amendment nor repeal of
this paragraph (a) nor the adoption of any provision of the Certificate of
Incorporation inconsistent with this paragraph (a) shall eliminate or reduce the
effect of this paragraph (a) in respect of any matter occurring, or any cause of
action, suit or claim that, but for this paragraph (a) of this Article, would
accrue or arise, prior to such amendment, repeal or adoption of an inconsistent
provision.


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                (b) The Corporation shall indemnify any person who was or is a
party or is threatened to be made a party to, or testifies in, any threatened,
pending or completed action, suit or proceeding, whether civil, criminal,
administrative or investigative in nature, by reason of the fact that such
person is or was a director, officer, employee or agent of the Corporation, or
is or was serving at the request of the Corporation as a director, officer,
employee or agent of another corporation, partnership, joint venture, employee
benefit plan, trust or other enterprise, against expenses (including attorneys'
fees), judgments, fines and amounts paid in settlement actually and reasonably
incurred by such person in connection with such action, suit or proceeding to
the full extent permitted by law, and the Corporation may adopt By-laws or enter
into agreements with any such person for the purpose of providing for such
indemnification.

                IN WITNESS WHEREOF, the undersigned has duly executed this
Certificate of Incorporation on this 29th day of June, 1995.




                                               /s/ Shelley A. Sorkin
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                                               Shelley A. Sorkin
                                               Sole Incorporator









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