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                                                                     Exhibit 4.1


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                          RADNOR HOLDINGS CORPORATION
                                   as Issuer,

                             WINCUP HOLDINGS, INC.
                          RADNOR CHEMICAL CORPORATION
                              STYROCHEM U.S., INC.
                            RADNOR MANAGEMENT, INC.
                             RADNOR DELAWARE, INC.

                                 as Guarantors

                                      and

                           FIRST UNION NATIONAL BANK
                                   as Trustee
                              -------------------


                         FOURTH SUPPLEMENTAL INDENTURE


                           Dated as of July 16, 1998

         (Supplementing a Trust Indenture Dated as of December 5, 1996,
               as amended by a First Supplemental Indenture Dated
                  as of December 17, 1996, Second Supplemental
                   Indenture Dated as of October 15, 1997 and
                       Third Supplemental Trust Indenture
                            dated February 9, 1998)

                              -------------------

                                  $100,000,000

                           10% Senior Notes due 2003



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          THIS FOURTH SUPPLEMENTAL INDENTURE, dated as of the 16th day of July
1998, (this "Fourth Supplemental Indenture") is among RADNOR HOLDINGS
CORPORATION, a Delaware corporation (the "Company"), WINCUP HOLDINGS, INC., a
Delaware corporation, RADNOR CHEMICAL CORPORATION (formerly SP Acquisition Co.),
a Delaware corporation, STYROCHEM U.S., INC. (formerly StyroChem International,
Inc.), a Texas corporation, RADNOR MANAGEMENT, INC., a Delaware corporation and
RADNOR DELAWARE, INC., a Delaware corporation (collectively, the "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 December 5, 1996, as amended by a First Supplemental Indenture
dated December 17, 1996, a Second Supplemental Indenture dated as of October 15,
1997 and a Third Supplemental Trust Indenture dated as of February 9, 1998 (as
amended, the "Indenture") relating to the creation by the Company of an issue of
$100,000,000 of its 10% 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);

          Each Foreign Subsidiary as of the date hereof was acquired by the
Company on or after the Issue Date (as such term is defined in the Indenture),
and accordingly, is a Restricted Subsidiary; and

          The Company, the Guarantors and the Trustee now desire to enter into
this Fourth Supplemental Indenture pursuant to Section 902 of the Indenture,
with the consent of the Holders of not less than a majority in aggregate
principal amount of the Outstanding Securities, by act of said Holders delivered
to the Company, each Guarantor and the Trustee, in order to (i) amend the
Indenture to conform the covenants of the Company provided for therein to
certain of the covenants of the Company set forth in the Indenture dated as of
October 15, 1997 entered into by the Company, the Guarantors and the Trustee
relating to the creation by the Company of an issue of $60,000,000 of its 10%
Series B Senior Notes due 2003 (the "Series B Indenture") and (ii) release
certain Foreign Subsidiaries from their guarantees of the Securities;

          Capitalized terms used herein without definition shall have the
meanings given such terms in the Indenture as amended by this Fourth
Supplemental Indenture.

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          NOW, THEREFORE, THIS FOURTH 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:

     SECTION 1 DEFINITIONS

          1.1  Amended Definitions.  The definitions of the following terms,
               -------------------                                          
which are defined in Section 101 of the Indenture, are amended and restated to
read as follows:

          (a) "Amended Credit Agreement" means the Second Amended and Restated
Credit and Security Agreement dated as of October 15, 1997 among the Company,
WinCup Holdings, Inc., Radnor Chemical Corporation (formerly SP Acquisition
Co.), and StyroChem U.S., Inc. (formerly StyroChem International, Inc.), as
borrowers("U.S. Borrowers") and BNY Financial Corporation (successor in interest
to the Bank of New York Commercial Corporation), as agent and lender, and the
supplement thereto, among StyroChem Europe (The Netherlands) B.V., StyroChem
Finland Oy, ThermiSol Denmark ApS, ThermiSol Finland Oy, and ThermiSol Sweden
AB, as borrowers, the U.S. Borrowers as guarantors and BNY Financial Ltd. as
agent and lender, dated as of December 12, 1997, as amended from time to time.

          (b) " Permitted Investment" means (i) any Investment in Cash
Equivalents, (ii) any Investment in the Company, (iii) Investments in existence
on the Issue Date, (iv) intercompany notes permitted under clause (f) of the
definition of "Permitted Indebtedness" in this Section 101, (v) Investments in
any Controlled Subsidiary or any Guarantor, or any Person which, as a result of
such Investment, becomes a Controlled Subsidiary or a Guarantor, and (vi)
Investments that do not at one time outstanding exceed $20,000,000 in joint
ventures, corporations, limited liability companies, partnerships or
Unrestricted Subsidiaries.

          (c) " Restricted Subsidiary" means (i) any Guarantor, (ii) any
Subsidiary of the Company in existence on the date hereof to which any line of
business or division (and the assets associated therewith) of any Guarantor are
transferred after the Issue Date, (iii) any Subsidiary of the Company organized
or acquired on or after the Issue Date, unless such Subsidiary has been
designated as an Unrestricted Subsidiary by a resolution of the Board of
Directors as provided in the definition of "Unrestricted Subsidiary" and (iv)
any Unrestricted Subsidiary which is designated as a Restricted Subsidiary by
the Board of Directors; provided, that immediately after giving 

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effect to any such designation (A) no Default of Event of Default has occurred
and is continuing and (B) in the case of any designation referred to in clause
(iii) or (iv) hereof, the Company could incur at least $1.00 of Indebtedness
pursuant to the covenant described in the initial paragraph under Section 1008
hereof, on a pro forma basis taking into account such designation. The Company
shall evidence any such designation to the Trustee by promptly filing with the
Trustee an officer's certificate certifying that such designation has been made
and complies with the requirements of the immediately preceding sentence.
Notwithstanding any provision of this Indenture to the contrary, each Guarantor
shall be a Restricted Subsidiary.

          1.2  New Definitions.  The following new definitions are added to
               ---------------                                             
Section 101 of the Indenture:

          (a) "Controlled Subsidiary" means a Restricted Subsidiary (i) 80% or
more of the total Equity Interests or other ownership interests of which (other
than directors' qualifying shares or shares required to be held by foreign
nationals, in each case to the extent mandated by applicable law) is at the time
owned by the Company (directly or through one or more Controlled Subsidiaries of
the Company) and (ii) of which the Company possesses, directly or indirectly,
the power to direct or cause the direction of the management or policies,
whether through the ownership of voting securities, by agreement or otherwise.

          (b) " Domestic Subsidiary" means, with respect to any Person, any
Subsidiary of such Person which is not incorporated or organized in any
jurisdiction outside of the United States of America.

          (c) " Foreign Subsidiary" means, with respect to any Person, any
Subsidiary of such Person other than a Domestic Subsidiary of such Person.


     SECTION 2 AMENDMENTS

          2.1  Events of Default.  Section 501 of the Indenture is amended and
               -----------------                                              
restated to read as follows:

          An "Event of Default" shall occur if:

          (1)  there shall be a default in the payment of interest on any
     Security when the same becomes due and payable and the Default continues
     for a period of thirty (30) days;

          (2)  there shall be a default in the payment of the principal of, or
     premium with respect to, any Security when 

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     the same becomes due and payable, at maturity, upon redemption, in
     connection with a Change of Control, an Asset Sale or otherwise;

          (3)  the Company or any Guarantor fails to observe or perform any
     covenant, condition or agreement on the part of the Company or such
     Guarantor to be observed or performed pursuant to Article Eight hereof;

          (4)  the Company or any Guarantor fails to observe or perform any
     covenant, condition or agreement on the part of the Company or such
     Guarantor to be observed or performed pursuant to Section 1006, 1008, 1009,
     1010, 1012, 1014, 1019 or 1020 hereof and such failure continues for a
     period of thirty (30) days;

          (5)  the Company or any Guarantor fails to observe or perform any
     other covenant, condition or agreement in this Indenture or the Securities
     and such failure continues for the period and after the notice specified
     below;

          (6)  the Company denies or disaffirms its obligations under this
     Indenture or the Securities;

          (7) a Guarantor denies or disaffirms its obligations under its
     Guarantee, or any Guarantee for any reason ceases to be, or is asserted in
     writing by any Guarantor or the Company not to be, in full force and effect
     and enforceable in accordance with its terms, except to the extent
     contemplated by this Indenture and any such Guarantee;

          (8)  a default occurs under any Indebtedness of the Company or any of
     its Subsidiaries (other than the Securities or the Guarantees), whether
     such Indebtedness now exists or is created after the Closing Date if either
     (A) such default results from the failure to pay the final scheduled
     principal installment in respect of any such Indebtedness on the stated
     maturity date thereof (after giving effect to any grace period) or (B) as a
     result of such default, the maturity of such Indebtedness has been
     accelerated prior to its express maturity and, in each case, the principal
     amount of such Indebtedness, together with the principal amount of all
     other Indebtedness with respect to which the principal amount remains
     unpaid at its final maturity (after giving effect to any grace period in
     respect of such final scheduled principal installment) or the maturity of
     which has been so accelerated, aggregates $5,000,000 or more;

          (9)  a final judgment or final judgments for the payment of money are
     entered by a court or courts of competent jurisdiction against the Company
     or any of its 

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     Restricted Subsidiaries and such judgment or judgments remain undischarged,
     unbonded or unstayed for a period of sixty (60) days, provided that the
     aggregate of all such judgments (other than any judgment as to which and
     only to the extent, a reputable insurance company has acknowledged coverage
     of such claim in writing) exceeds $5,000,000;

          (10)  the Company, any Guarantor or any other Restricted Subsidiary
     pursuant to or within the meaning of any Bankruptcy Law:

               (a)  commences a voluntary case,

               (b)  consents to the entry of an order for relief against it in
     an involuntary case in which it is a debtor,

               (c)  consents to the appointment of a Custodian of it or for all
     or substantially all of its property,

               (d)  makes a general assignment for the benefit of its creditors,
     or

               (e) admits in writing its inability to pay debts as the same
     become due; or

          (11)  a court of competent jurisdiction enters an order or decree
     under any Bankruptcy Law that:

               (a) is for relief against the Company, any Guarantor or any other
     Restricted Subsidiary in an involuntary case in which it is a debtor,

               (b) appoints a Custodian of the Company, any Guarantor or any
     other Restricted Subsidiary or for all or substantially all of their
     property,

               (c) orders the liquidation of the Company, any Guarantor or any
     other Restricted Subsidiary,

     and the order or decree remains unstayed and in effect for sixty (60) days.

          The term "Custodian" means any receiver, trustee, assignee, liquidator
or similar official under any Bankruptcy Law.

          A Default under clause (5) is not an Event of Default until the
Trustee notifies the Company, or the Holders of at least 25% in principal amount
of the Securities then Outstanding notify the Company and the Trustee, of the
Default and the Company does not cure the Default within sixty (60) days after

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receipt of such notice.  The notice must specify the Default, demand that it be
remedied and state that the notice is a "Notice of Default."

          The failure to make any payment on the Securities when due shall,
after the expiration date of any applicable grace period, constitute an Event of
Default under this Indenture.

          2.2  Cross References.  References in this Indenture to clauses (9)
               ----------------                                              
and (10) of Section 501 shall be deemed to refer instead to clauses (10) and
(11) of Section 501.

          2.3  Subsidiary Guarantees.  Section 1019 of the Indenture is amended
               ---------------------                                           
to read as follows:

          (a)  If (i) any Domestic Subsidiary of the Company becomes a
Restricted Subsidiary after the Issue Date, (ii) the Company or any Subsidiary
of the Company that is a Guarantor transfers or causes to be transferred, in one
transaction or a series of related transactions, property or assets (including,
without limitation, businesses, divisions, real property, assets or equipment)
which in the aggregate have a value equal to or greater than 15% of the
Company's total assets determined on a consolidated basis as of the time of
transfer to any Subsidiary or Subsidiaries of the Company that is not a
Guarantor or are not Guarantors, or (iii) any Domestic Subsidiary of the Company
which has a value equal to or greater than 5% of the Company's total assets
determined on a consolidated basis as of the time of determination directly or
indirectly guarantees any Senior Indebtedness of the Company, or (iv) any
Foreign Subsidiary of the Company which has a value equal to or greater than 5%
of the Company's total assets determined on a consolidated basis as of the time
of determination and is not a Guarantor (x) directly or indirectly guarantees
any Senior Indebtedness of the Company or (y) causes more than two-thirds of its
Capital Stock to be pledged to secure any Senior Indebtedness of the Company,
the Company shall cause such Subsidiary or Subsidiaries to execute and deliver
to the Trustee a supplemental indenture pursuant to which such Subsidiary or
Subsidiaries shall unconditionally guarantee, in accordance with Article
Thirteen hereof, all of the Company's obligations under the Indenture and the
Securities on the same terms as the other Guarantors, which Guarantee shall rank
pari passu with any Senior Indebtedness of such Subsidiary. The provisions of
clauses (ii) and (iii) of this paragraph shall not apply to any transaction
permitted by Section 1009.  The Company may, at its option, cause any Subsidiary
of the Company which is a Foreign Subsidiary to execute and deliver a Guarantee
in accordance with the provisions of Article XIII of this Indenture.

          (b)  Each guarantee created pursuant to the provisions described in
the foregoing paragraph is referred to as 

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a "Guarantee" and the issuer of each such Guarantee is referred to as a
"Guarantor." Notwithstanding the foregoing, any Guarantee shall be automatically
and unconditionally released and discharged upon (i) any sale, exchange,
transfer or other disposition (by way of merger, consolidation or otherwise), to
any Person(provided, that if such Person is a Guarantor, the Guarantee of such
Person shall not also be released and discharged) of all of the Equity Interests
of any Guarantor, or all or substantially all of the assets of any Guarantor,
which is in compliance with this Indenture, or (ii) the release of the guarantee
or other obligation of any Guarantor with respect to any other Senior
Indebtedness of the Company which caused such Guarantor to guarantee the
Company's obligations under this Indenture and the Securities in accordance with
clause (iii) or (iv) of paragraph (a) of this section.

     SECTION 3 RELEASE OF FOREIGN SUBSIDIARIES

          3.1  In accordance with the requirements of Section 1019 of the
Indenture, prior to its amendment by this Fourth Supplemental Indenture,
StyroChem International, Ltd., StyroChem Europe (The Netherlands) B.V.,
StyroChem Finland OY, Thermisol Finland OY, Thermisol Denmark APS, and Thermisol
Sweden AB (collectively, the "Foreign Guarantors") guaranteed all of the
Indenture Obligations pursuant to, in the case of StyroChem International, Ltd.,
the Indenture, and, in the case of the other Foreign Guarantors, a Second
Supplemental Indenture dated as of October 15, 1997 (the "Second Supplemental
Indenture") executed and delivered by certain of the Foreign Guarantors to the
Trustee.  The Indenture, as amended by this Fourth Supplemental Indenture, does
not require the Foreign Guarantors to guarantee the Indenture Obligations.
Accordingly, the Company has requested, and the Trustee hereby agrees, pursuant
to the consent of the Holders of not less than a majority in aggregate principal
amount of the Outstanding Securities, that the Foreign Guarantors are released
from the Indenture and the Second Supplemental Indenture and from all
obligations and liabilities in connection with their guarantee of the Indenture
Obligations under the Indenture, effective as of October 15, 1997.

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

                                         RADNOR HOLDINGS CORPORATION
                              
                              
Attest:/s/ CJWilliamson                  By: /s/  Michael T. Kennedy
       ---------------------                ------------------------
       Name:  CJWilliamson                     Michael T. Kennedy
       Title:  Secretary                       President
                              
                              
                                         WINCUP HOLDINGS, INC.
                              
                              
Attest:/s/ CJWilliamson                  By: /s/  Michael T. Kennedy
       ---------------------                ------------------------
       Name:  CJWilliamson                     Michael T. Kennedy
       Title:  Secretary                       President
                              
                              
                                         RADNOR CHEMICAL CORPORATION
                              
                              
Attest:/s/ CJWilliamson                  By: /s/  Michael T. Kennedy
       ---------------------                ------------------------
       Name:  CJWilliamson                     Michael T. Kennedy
       Title:  Secretary                       President
                              
                              
                              
                                         STYROCHEM U.S., INC.
                              
                              
Attest:/s/ CJWilliamson                  By: /s/  Michael T. Kennedy
       ---------------------                ------------------------
       Name:  CJWilliamson                     Michael T. Kennedy
       Title:  Secretary                       President
                              
                              
                                         RADNOR MANAGEMENT, INC.
                              
                              
Attest:/s/ CJWilliamson                  By: /s/  Michael T. Kennedy
       ---------------------                ------------------------
       Name:  CJWilliamson                     Michael T. Kennedy
       Title:  Secretary                       President
                              
                              
                              

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                                         RADNOR DELAWARE, INC.
                              
                              
Attest:/s/ CJWilliamson                  By: /s/  Michael T. Kennedy
       ---------------------                ------------------------
       Name:  CJWilliamson                     Michael T. Kennedy
       Title:  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:  C.T.O.                          Assistant Vice President

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