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                                                                    EXHIBIT 4.10
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                          RADNOR HOLDINGS CORPORATION
                                  as Issuer,

                             WINCUP HOLDINGS, INC.
                          RADNOR CHEMICAL CORPORATION
                             RADNOR DELAWARE, INC.
                            RADNOR MANAGEMENT, INC.
                             STYROCHEM U.S., LTD.
                              WINCUP TEXAS, LTD.
                             STYROCHEM GP, L.L.C.
                             STYROCHEM LP, L.L.C.
                               WINCUP GP, L.L.C.
                                      and
                               WINCUP LP, L.L.C.

                                 as Guarantors

                                      and

                           FIRST UNION NATIONAL BANK
                                  as Trustee

                                        
                                        
                         SECOND SUPPLEMENTAL INDENTURE

                         Dated as of January 21, 1999

         (Supplementing a Trust Indenture dated as of October 15, 1997
           as amended by a First Supplemental Indenture dated as of
                               February 9, 1998)

                               _________________
                                        
                                  $60,000,000

                      10% Series B Senior Notes due 2003

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     THIS SECOND SUPPLEMENTAL INDENTURE, dated as of the 21st day of January,
1999 (this "Second Supplemental Indenture"), is among RADNOR HOLDINGS
CORPORATION, a Delaware corporation (the "Company"), WINCUP HOLDINGS, INC., a
Delaware corporation, RADNOR CHEMICAL CORPORATION (formerly known as SP
Acquisition Co.), a Delaware corporation, RADNOR DELAWARE, INC., a Delaware
corporation, RADNOR MANAGEMENT, INC., a Delaware corporation and STYROCHEM U.S.,
LTD. (formerly known as StyroChem International, Inc. and StyroChem U.S., Inc.),
a Texas limited partnership, (collectively, the "Guarantors"), WINCUP TEXAS,
LTD., a Texas limited partnership, STYROCHEM GP, L.L.C., a Delaware limited
liability company, STYROCHEM LP, L.L.C., a Delaware limited liability company,
WINCUP GP, L.L.C., a Delaware limited liability company and WINCUP LP, L.L.C., a
Delaware limited liability company, (collectively, the "New Guarantors") and
FIRST UNION NATIONAL BANK, as trustee (the "Trustee").

                                   RECITALS:

     The Company, the Guarantors and the Trustee are parties to a certain
Indenture dated October 15, 1997, as amended by a First Supplemental Indenture
dated as of February 9, 1998 (as amended, the "Indenture") relating to the
creation by the Company of an issue of $60,000,000 of its 10% Series B Senior
Notes, due 2003 (the "Securities");

     Each Guarantor has issued a guarantee of the Securities (collectively, the
"Guarantees") pursuant to which the Guarantors have guaranteed, in accordance
with Article Thirteen of the Indenture, all Indenture Obligations (as such term
is defined in the Indenture); and

     The Company, the Guarantors, the New Guarantors and the Trustee now desire
to enter into this First Supplemental Indenture pursuant to Section 901(vi) of
the Indenture, without the consent of the Holders, in order to add the New
Guarantors as Guarantors and Restricted Subsidiaries under the Indenture;

     Capitalized terms used herein without definition shall have the meanings
given such terms in the Indenture.

         NOW, THEREFORE, THIS FIRST SUPPLEMENTAL INDENTURE WITNESSETH:

     For and in consideration of the premises and for other good and valuable
consideration, it is covenanted and agreed, for the benefit of each other and
for the equal and proportionate benefit of the Holders of the Securities issued
under the Indenture, as follows:

                                  ARTICLE ONE

                  JOINDER AND GUARANTEE OF THE NEW GUARANTORS

     Section 101. The New Guarantors hereby absolutely, unconditionally and
irrevocably guarantee, on a joint and several basis with the Guarantors, to the
Trustee and the Holders, as if each New Guarantor was the principal debtor, the
punctual payment and performance when due of all Indenture Obligations (which
for purposes of this Guarantee shall also be deemed 

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to include all commissions, fees, charges, costs and expenses (including
reasonable legal fees and disbursements of one counsel) arising out of or
incurred by the Trustee or the Holders in connection with the enforcement of
this Guarantee). This Guarantee shall rank pari passu with any Senior
Indebtedness of the New Guarantors and shall be subject in all respects to, and
governed by all of the terms and provisions applicable to Guarantees in, the
Indenture, including without limitation Article Thirteen thereof.

     Section 102.  As of the date hereof, all references to the "Guarantors" in
the Indenture shall be deemed to refer collectively to: (i) the Guarantors in
existence on the date hereof and (ii) the New Guarantors.

     IN WITNESS WHEREOF, the parties hereto have caused this Second Supplemental
Indenture to be duly executed, all as of the day and year first above written.

                                        RADNOR HOLDINGS CORPORATION


Attest: /s/ Caroline J. Williamson      By: /s/ Michael T. Kennedy
        --------------------------          ----------------------------------
        Caroline J. Williamson              Michael T. Kennedy
        Secretary                           President


                                        WINCUP HOLDINGS, INC.


Attest: /s/ Caroline J. Williamson      By: /s/ Michael T. Kennedy
        --------------------------          ----------------------------------
        Caroline J. Williamson              Michael T. Kennedy
        Secretary                           President


                                        RADNOR CHEMICAL CORPORATION


Attest: /s/ Caroline J. Williamson      By: /s/ Michael T. Kennedy
        --------------------------          ----------------------------------
        Caroline J. Williamson              Michael T. Kennedy
        Secretary                           President


                                        RADNOR DELAWARE, INC.


Attest: /s/ Caroline J. Williamson      By: /s/ Michael T. Kennedy
        --------------------------          ----------------------------------
        Caroline J. Williamson              Michael T. Kennedy
        Secretary                           President

                                       3
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                                        RADNOR MANAGEMENT, INC.


Attest: /s/ Caroline J. Williamson      By: /s/ Michael T. Kennedy
        --------------------------          ----------------------------------
        Caroline J. Williamson              Michael T. Kennedy
        Secretary                           President


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


Attest: /s/ Caroline J. Williamson      By: /s/ Michael T. Kennedy
        --------------------------          ----------------------------------
        Caroline J. Williamson              Michael T. Kennedy
        Secretary                           President


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


Attest: /s/ Caroline J. Williamson      By: /s/ Michael T. Kennedy
        --------------------------          ----------------------------------
        Caroline J. Williamson              Michael T. Kennedy
        Secretary                           President


                                        STYROCHEM GP, L.L.C.
                                        By: Radnor Chemical Corporation,
                                              its sole member


Attest: /s/ Caroline J. Williamson      By: /s/ Michael T. Kennedy
        --------------------------          ----------------------------------
        Caroline J. Williamson              Michael T. Kennedy
        Secretary                           President

                                       4
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                                       STYROCHEM LP, L.L.C.
                                        By: Radnor Chemical Corporation,
                                              its sole member


Attest: /s/ Caroline J. Williamson      By: /s/ Michael T. Kennedy
        --------------------------          ----------------------------------
        Caroline J. Williamson              Michael T. Kennedy
        Secretary                           President

 
                                        WINCUP GP, L.L.C.
                                        By: WinCup Holdings, Inc.,
                                              its sole member


Attest: /s/ Caroline J. Williamson      By: /s/ Michael T. Kennedy
        --------------------------          ----------------------------------
        Caroline J. Williamson              Michael T. Kennedy
        Secretary                           President


                                        WINCUP LP, L.L.C.
                                        By: WinCup Holdings, Inc.,
                                              its sole member


Attest: /s/ Caroline J. Williamson      By: /s/ Michael T. Kennedy
        --------------------------          ----------------------------------
        Caroline J. Williamson              Michael T. Kennedy
        Secretary                           President

               
                                        FIRST UNION NATIONAL BANK,
                                        as Trustee


Attest: /s/ Ralph E. Jones              By:  /s/ Alan G. Finn
        --------------------------          ----------------------------------
        Name: Ralph E. Jones                Alan G. Finn
        Title: Corporate Trust Officer      Assistant Vice President

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