<PAGE>

                                 AMENDMENT NO. 1

                                       TO

                      THIRD AMENDED AND RESTATED REVOLVING
                          CREDIT AND SECURITY AGREEMENT

     THIS AMENDMENT NO. 1 (the "Amendment") is entered into as of March 13,
2000, by and among WinCup Holdings, Inc., Radnor Chemical Corporation, StyroChem
U.S., Ltd., Radnor Holdings Corporation ("Radnor"), Radnor Delaware, Inc.,
StyroChem Delaware, Inc. and WinCup Texas, Ltd. (collectively, the "U.S.
Borrowers"), StyroChem Europe (the Netherlands) B.V., StyroChem Finland Oy,
ThermiSol Denmark A/S, ThermiSol Sweden AB and ThermiSol Finland Oy
(collectively, the "European Borrowers", and together with the U.S. Borrowers,
the "Borrowers"), Bank of America, N.A. ("Bank of America") and each of the
other financial institutions which are or become parties hereto (collectively,
the "Lenders") and Bank of America, as administrative and collateral agent for
the Lenders (in such capacity, the "Agent").

                                   BACKGROUND

     The Borrowers, the Lenders and the Agent are parties to a Third Amended and
Restated Revolving Credit and Security Agreement dated as of December 29, 1999
(as amended, and as may be further amended, supplemented or otherwise modified
from time to time, the "Loan Agreement") pursuant to which the Lenders provide
the Borrowers with certain financial accommodations.

     The Borrowers have requested certain modifications to the Loan Agreement.
Such modifications require the consent of the Required Lenders (as defined in
the Loan Agreement). The Required Lenders have consented to the requested
modifications on the terms and conditions hereafter set forth.

     NOW THEREFORE, in consideration of any loan or advance or grant of credit
heretofore or hereafter made to or for the account of the Borrowers by any
Lender and the Agent, and for other good and valuable consideration, the receipt
and sufficiency of which are hereby acknowledged, the parties hereto hereby
agree as follows.

     1. Definitions. All capitalized terms not otherwise defined herein shall
        -----------
have the meanings given to them in the Loan Agreement.

     2. Amendment to Loan Agreement. Subject to satisfaction of the conditions
        ---------------------------
precedent set forth in Section 3 below, the Loan Agreement is hereby amended as
follows:

        (a) Section 1.2 of the Loan Agreement is hereby amended by amending the
following defined term in its entirety as follows:

        "Maximum European Loan Amount" shall mean $7,000,000.
         ----------------------------
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        (b) Section 1.2 of the Loan Agreement is hereby amended by amending the
following defined term in its entirety as follows:

        "Maximum U.S. Loan Amount" shall mean $33,000,000.
         ------------------------

        (c) Section 1.2 of the Loan Agreement is hereby amended by amending the
following defined term in its entirety as follows:

        "Net Worth" at a particular date, shall mean the aggregate amount of all
        assets of Radnor on a Consolidated Basis as may properly be classified
        as such in accordance with GAAP consistently applied and such other
        assets as are properly classified as "intangible assets", less the
        aggregate amount of all Indebtedness of Radnor on a Consolidated Basis.
        Notwithstanding the foregoing, foreign currency translation adjustments
        reducing the carrying value of the net assets not in excess of
        $15,000,000 will be excluded from such calculation of Net Worth.

     3. Conditions of Effectiveness. This Amendment shall become effective upon
        ---------------------------
satisfaction of the following conditions precedent:

        (a) the receipt by the Agent, on behalf of the Lenders, of four (4)
copies of this Amendment executed by the Borrowers and the Required Lenders; and

        (b) the Borrowers shall have paid an amendment fee to each Lender party
to this Amendment in the amount of $2500.

     4. Representations and Warranties. Each of the Borrowers hereby represents
        ------------------------------
and warrants as follows:

        (a) It has taken all necessary action to authorize the execution,
delivery and performance of this Amendment;

        (b) This Amendment has been duly executed and delivered by such Borrower
and constitutes such Borrower's legal, valid and binding obligation, enforceable
in accordance with its terms.

        (c) No consent, approval, authorization or order of, or filing,
registration or qualification with, any court or governmental authority or third
party is required in connection with the execution, delivery or performance by
such Borrower of this Amendment.

        (d) The representations and warranties of the Borrowers set forth in the
Loan Agreement are true and correct as of the date hereof (except those that
expressly relate

                                      -2-
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to an earlier date) and all provisions of the Loan Agreement and the Other
Documents, except as amended hereby, are in full force and effect.

        (e) No Event of Default or Default has occurred and is continuing or
would exist after giving effect to this Amendment.

        (f) Such Borrower has no defenses, counterclaims or offsets with respect
to the Loan Agreement and its performance of its obligations thereunder, or if
such Borrower has any such defenses, claims, counterclaims or offsets to the
Loan Agreement or the Other Documents or any transaction related to the Loan
Agreement or the Other Documents, the same are hereby waived, relinquished and
released in consideration of the Required Lender's execution and delivery of
this Amendment.

     5. Effect on the Loan Agreement.
        ----------------------------

        (a) Upon the effectiveness of this Amendment, each reference in the Loan
Agreement to "this Agreement," "hereunder," "hereof," "herein" or words of like
import shall mean and be a reference to the Loan Agreement, as amended hereby.
The Other Documents, now or hereafter executed and delivered pursuant to the
terms of the Loan Agreement are hereby amended so that any reference to the Loan
Agreement shall mean a reference to the Loan Agreement as amended hereby.

        (b) Except as specifically amended herein, the Loan Agreement and the
Other Documents, now or hereafter executed and delivered pursuant to the terms
of the Loan Agreement, shall remain in full force and effect, and are hereby
ratified and confirmed.

        (c) The execution, delivery and effectiveness of this Amendment shall
not operate as a waiver of any right, power or remedy of any Lender or the
Agent, nor constitute a waiver of any provision of the Loan Agreement or the
Other Documents executed and/or delivered under or on connection therewith.

     6. Governing Law. This Amendment shall be binding upon and inure to the
        -------------
benefit of the parties hereto and their respective successors and assigns and
shall be governed by and construed in accordance with the laws of the State of
New York.

     7. Headings. Section headings in this Amendment are included herein for
        --------
convenience of reference only and shall not constitute a part of this Amendment
for any other purpose.

     8. Counterparts, Telecopied Signatures. This Amendment may be executed in
        -----------------------------------
any number of and by different parties hereto, on separate counterparts, all of
which when so executed shall be deemed an original, but all such counterparts
shall constitute one and the same agreement. Any signature delivered by a party
by facsimile transmission shall be deemed to be an original signature hereto.

                                      -3-
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     9. Expenses. Each of the Borrowers, jointly and severally, agrees to pay
        --------
all reasonable costs and expenses incurred in connection with the negotiation,
execution and delivery of this Amendment, including the reasonable fees and
expenses of the Agent's legal counsel.

     10. ENTIRETY. THIS AMENDMENT, THE LOAN AGREEMENT AND THE OTHER DOCUMENTS
         --------
EMBODY THE ENTIRE AGREEMENT BETWEEN THE PARTIES AND SUPERSEDE ALL PRIOR
AGREEMENTS AND UNDERSTANDINGS, IF ANY, RELATING TO THE SUBJECT MATTER HEREOF.
THIS AMENDMENT, THE LOAN AGREEMENT AND THE OTHER DOCUMENTS REPRESENT THE FINAL
AGREEMENT BETWEEN THE PARTIES AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR,
CONTEMPORANEOUS OR SUBSEQUENT ORAL AGREEMENTS OF THE PARTIES.

                                      -4-
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     IN WITNESS WHEREOF, this Amendment has been duly executed as of the day and
year first written above.


U.S. BORROWERS:                 WINCUP HOLDINGS, INC.


                                By:
                                   ---------------------------------------------


                                RADNOR CHEMICAL CORPORATION


                                By:
                                   ---------------------------------------------



                                STYROCHEM U.S., LTD.
                                By its general partner, StyroChem GP, L.L.C.
                                By its sole member, Radnor Chemical Corporation


                                By:
                                   ---------------------------------------------


                                RADNOR HOLDINGS CORPORATION


                                By:
                                   ---------------------------------------------


                                RADNOR DELAWARE, INC.


                                By:
                                   ---------------------------------------------


                                STYROCHEM DELAWARE, INC.


                                By:
                                   ---------------------------------------------

                                      -5-
<PAGE>

                                WINCUP TEXAS, LTD.
                                By its general partner, WinCup GP,
                                L.L.C. By its sole member WinCup
                                Holdings, Inc.

                                By:
                                   ---------------------------------------------


EUROPEAN BORROWERS:             STYROCHEM EUROPE (THE NETHERLANDS) B.V.


                                By:
                                   ---------------------------------------------


                                STYROCHEM FINLAND OY


                                By:
                                   ---------------------------------------------


                                THERMISOL DENMARK A/S


                                By:
                                   ---------------------------------------------


                                THERMISOL SWEDEN AB


                                By:
                                   ---------------------------------------------


                                THERMISOL FINLAND OY.


                                By:
                                   ---------------------------------------------

                                      -6-
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AGENT AND LENDERS:              BANK OF AMERICA, N.A.
                                as Agent and a Lender


                                By:
                                   ---------------------------------------------
                                Name:
                                     -------------------------------------------
                                Title:
                                      ------------------------------------------

                                FIRST UNION NATIONAL BANK,
                                as a Lender


                                By:
                                   ---------------------------------------------
                                Name:
                                     -------------------------------------------
                                Title:
                                      ------------------------------------------

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