<PAGE>

                                                                    Exhibit 4(n)

                      SIXTH AMENDMENT, WAIVER AND CONSENT
                           DATED AS OF JUNE 21, 2001
               TO CREDIT AGREEMENT DATED AS OF DECEMBER 12, 1997

          This Sixth Amendment, Waiver and Consent (this "Amendment"), dated as
of June 21, 2001, is made by and among MATERIAL SCIENCES CORPORATION, a Delaware
corporation (the "Company"), the financial institutions party hereto (the
"Banks"), and Bank of America, N.A., as agent for the Banks (in such capacity,
the "Agent").  Unless otherwise defined, terms defined in the Credit Agreement
shall have the same respective meanings when used herein.

                              W I T N E S S E T H:
                              - - - - - - - - - -

     WHEREAS, the Company, the Banks and the Agent are parties to that certain
Credit Agreement, dated as of December 12, 1997 (as amended or modified and in
effect on the date hereof, the "Credit Agreement");

     WHEREAS, the Company has requested that the Banks and the Agent agree to
amend or modify the Credit Agreement as set forth herein; and

     WHEREAS, the Banks and the Agent are willing to amend or modify the Credit
Agreement on the terms and conditions contained herein.

     NOW, THEREFORE, in consideration of the premises, the mutual covenants
herein contained and other good and valuable consideration (the receipt,
adequacy and sufficiency of which is hereby acknowledged), the parties hereto,
intending legally to be bound, hereby agree as follows:

                                   ARTICLE I

                                  AMENDMENTS
                                  ----------

     The Credit Agreement is amended as follows:

     1.1. Article I of the Credit Agreement is amended so that the last
sentence of the definition of "Applicable Margin" shall read in its entirety as
follows:

             "Applicable Margin" means, in the case of Base Rate
              -----------------
             Loans, 1.75% per annum, in the case of Offshore Rate
             Loans, 3.25% per annum, and in the case of the
             Commitment Fee, 0.50% per annum.

     1.2. Article I of the Credit Agreement is amended so that the definition
of Bekaert shall read as follows:
<PAGE>

            "Bekaert" means Bekaert corporation, a Delaware corporation.
             -------

     1.3. Article I of the Credit Agreement is further amended so as to add
the following definitions.

            "MSC/SFI Agreements" means the MSC/SFI Contribution Agreement and
             ------------------
     the MSC/SFI Purchase Agreement and the other agreements referred to
     therein.

            "MSC/SFI Closing" means the closing under the MSC/SFI Purchase
             ---------------
     Agreement.

            "MSC/SFI Contribution Agreement" means the Contribution Agreement
             ------------------------------
     dated as of June 29, 2001, among the Company, MSC/SFI and New SFI.

            "MSC/SFI Gross Cash Proceeds" means cash proceeds received by the
             ---------------------------
     Company (or MSC/SFI) from the MSC/SFI Closing before taxes and expenses.

            "MSC/SFI Purchase Agreement" means the Purchase Agreement dated as
             --------------------------
     of June 10, 2001 among the Company, MSC/SFI, Bekaert, and NVB.

            "MSC/SFI Transaction" means collectively the transactions provided
             -------------------
     for in the MSC/SFI Agreements.

            "New SFI" means New SFI, LLC, a Delaware limited liability company.
             -------

            "NVB" means N.V. Bekaert S.A., a Belgium corporation.
             ---

     1.4. Section 10.1 of the Credit Agreement is amended by substituting "; or"
for the period at the end of subsection (m) and by adding subsection (n) as
follows:

            (n)   New Financial Covenants. On or before August 31, 2001 the
                  -----------------------
     Company shall have failed to execute an amendment to this Agreement which
     shall revise, to the satisfaction of the Banks, the financial tests
     specified in Sections 9.1, 9.2 and 9.3 and shall otherwise be in all
     respects acceptable to the Banks.

                                  ARTICLE II

                                    WAIVER
                                    ------

     2.1. The Banks hereby waive for the period from June 1, 2001 through
August 31, 2001 compliance by the Company with the provisions of Sections 9.1
(Minimum Net Worth), 9.2 (Consolidated Debt to Adjusted EBITDA Ratio) and 9.3
(Fixed Charge Coverage Ratio) of the Credit Agreement.  It is understood that
the foregoing waiver does not apply to any computation date or period after
August 31, 2001.

     2.2. The foregoing waiver is specific in time and in intent and does not
constitute, nor shall it be construed as, a waiver of any other right, power or
privilege under the Credit Agreement, or under any agreement, contract,
indenture, document or other instrument mentioned in the Credit Agreement; nor
does the foregoing waiver preclude other or further

                                      -2-
<PAGE>

exercise of any other right, power or privilege, nor shall the waiver of any
right, power, privilege or default hereunder, or under any agreement, contract,
indenture, document, or instrument mentioned in the Credit Agreement, constitute
a waiver of any other default of any other term or provision.

                                  ARTICLE III

                                    CONSENT
                                    -------

     3.1. The MSC/SFI Transaction.  The Company represents to the Agent and the
          -----------------------
Banks that:

     (a)  MSC/SFI is a wholly-owned Subsidiary of the Company.

     (b)  As of the date hereof, MSC/SFI owns 50% of ISF.

     (c)  Two of MSC/SFI's wholly owned subsidiaries, Pro Marketing, Inc., a
Nebraska corporation ("Pro Marketing"), and Solar-Gard International, Inc., a
Florida corporation ("Solar-Gard"), have been merged with and into MSC/SFI.
MSC/SFI is the surviving entity.  As a result of the Solar-Gard merger, MSC/SFI
will own all of the equity in MSC Specialty Films (UK) Ltd., a United Kingdom
corporation, Solar Gard (SEA) Pte, Ltd., a Singapore corporation, and MSC
Specialty Films (Canada) Inc., an Ontario corporation.

     (d)  MSC/SFI has formed New SFI as a wholly owned subsidiary of MSC/SFI.
Pursuant to the MSC/SFI Contribution Agreement, MSC/SFI will contribute the
Business through the contribution of substantially all of its assets (including
the assets that were formerly owned by Pro Marketing and Solar-Gard) to New SFI.

     (e)  Pursuant to the MSC/SFI Contribution Agreement, MSC/SFI will transfer
to New SFI the stock of the following wholly owned subsidiaries: MSC Specialty
Films (Australasia) Pty. Limited, an Australian corporation, MSC Specialty Films
(UK) Ltd., a United Kingdom company, Solar-Gard (SEA), Pte, Ltd., a Singapore
company, MSC Specialty Films (Canada) Inc., an Ontario corporation, MSC
Specialty Films de Mexico S.A. de C.V., a Mexican corporation, and Specialty
Films de Services Company S.A. de C.V., a Mexican corporation, except that 1% of
the stock of each of MSC Specialty Films de Mexico S.A. de C.V. and Specialty
Films de Services Company S.A. de C.V. has been transferred to MSC Specialty
Films (Canada), Inc., an Ontario corporation, prior to the merger of Solar-Gard
into MSC/SFI.

     (f)  Pursuant to the MSC/SFI Purchase Agreement, MSC/SFI will sell to
Bekaert all of MSC/SFI's right, title and interest in and to its membership
interest in ISF and Newco, all subject to the terms and conditions set forth
therein.

     (g)  Pursuant to the MSC/SFI Purchase Agreement, MSC/SFI will sell to NVB
(or its designated Affiliate) all of MSC/SFI's right, title and interest in and
to certain intellectual property and MSC will assign to NVB a certain agreement
with Research Frontiers Incorporated, all subject to the terms and conditions
set forth therein.

     (h)  The Company has furnished to the Banks a true and correct copy of the
MSC/SFI

                                      -3-
<PAGE>

Agreements substantially in the form as executed or to be executed.

     (i)  The MSC/SFI Gross Cash Proceeds shall not be less than $120,000,000.

     3.2. Consent.  Notwithstanding the provisions of Article VIII of the Credit
          -------
Agreement, the Banks hereby consent to the MSC/SFI Transaction, provided,
                                                                --------
however that:
-------

     (a)  the MSC/SFI Closing shall occur on or before July 31, 2001,

     (b)  concurrent with the MSC/SFI Closing, the Company shall receive MSC/SFI
Gross Cash Proceeds in immediately available funds of not less than
$120,000,000,

     (c)  the Company shall immediately apply all of such MSC/SFI Gross Cash
Proceeds to the payment in full of the Revolving Loans, and

     (d)  concurrent with the MSC/SFI Closing, the Combined Commitment shall
automatically reduce to $20,000,000 (such reduction to be pro rata among the
Banks according to their respective Commitments).

     3.3. Release. The Banks further agree that concurrent with the MSC/SFI
          -------
Closing, the Guaranties executed by MSC/SFI, Solar-Gard and New SFI pursuant to
the Credit Agreement and any amendments thereto shall automatically be deemed to
have been released and terminated in all respects and any and all liabilities of
MSC/SFI, Solar-Gard and New SFI arising under or otherwise related to the Credit
Agreement are also hereby released.

                                   ARTICLE IV

                        REPRESENTATIONS AND WARRANTIES
                        ------------------------------

     The Company hereby represents and warrants to the Banks and the Agent that:

     4.1. Authorization, etc.  The execution, delivery and performance of this
          ------------------
Amendment are within the Company's corporate authority, have been duly
authorized by all necessary corporate action, have received all necessary
consents and approvals (if any shall be required), and do not and will not
contravene or conflict with any provision of law or of the Certificate of
Incorporation or By-laws of the Company or its Subsidiaries, or of any other
agreement binding upon the Company or its Subsidiaries or their respective
property.

     4.2. Validity.  This Amendment constitutes the legal, valid, and binding
          --------
obligations of the Company, enforceable against the Company in accordance with
its terms, except as enforceability may be limited by applicable bankruptcy,
insolvency, or similar laws affecting the enforcement of creditors' rights
generally or by equitable principles relating to enforceability.

     4.3. No Default.  Except for any Default or Event of Default which will be
          ----------
cured by this Amendment becoming effective, no Event of Default has occurred and
is continuing or will result from this Amendment.

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                                   ARTICLE V

                             CONDITIONS PRECEDENT
                             --------------------

     This Amendment shall become effective as of June 21, 2001 (the "Effective
Date"), subject, however, to the receipt by the Agent of the following in form
and substance satisfactory to the Agent:

     5.1. Counterparts. Counterparts of this Amendment (or an executed facsimile
          ------------
copy hereof), executed by the Company and the Banks.

     5.2. Fees and Expenses. Evidence of the payment to the Agent in immediately
          -----------------
available funds of all legal fees and expenses of the Agent to the extent
theretofore invoiced.

     5.3. Resolutions, etc.  A certificate of the Secretary or the Assistant
          ----------------
Secretary of the Company as to resolutions, and the signatures and incumbency of
officers authorized to sign this Amendment.

     5.4. Opinion. An opinion of Kirkland & Ellis, counsel to the Company, as to
          -------
the due authorization execution and delivery by the Company of this Amendment.

     5.5. MSC/SFI Agreements.  A certified copy of the MSC/SFI Agreements
          ------------------
substantially in the form as executed or to be executed.

                                   ARTICLE VI

                                 MISCELLANEOUS
                                 -------------

     6.1. Documents Remain in Effect.  Except as amended or modified by this
          --------------------------
Amendment, the Credit Agreement remains in full force and effect and the Company
confirms that its representations, warranties, agreements and covenants
contained in, and obligations and liabilities under, the Credit Agreement and
each of the other Loan Documents are true and correct in all material respects
as if made on the date hereof, except where such representation, warranty,
agreement or covenant speaks as of a specified date.  References to the Credit
Agreement in any other document shall be deemed to include a reference to the
Credit Agreement as amended or modified hereby, whether or not reference is made
to this Amendment.

     6.2. Expenses. The Company covenants to pay to or reimburse the Agent, upon
          --------
demand, for all reasonable costs and expenses (including legal expenses) in
connection with the development, preparation, negotiation, execution and
delivery of this Amendment and the Loan Documents.

     6.3. Headings. Section headings used in this Amendment are for convenience
          --------
of reference only, and shall not affect the construction of this Amendment.

     6.4. Governing Law. This Amendment shall be a contract made under and
          -------------
governed by the internal laws of the State of Illinois, without giving effect to
principles of conflicts of

                                      -5-
<PAGE>

laws.

     6.5.  Cumulative Rights. All obligations of the Company and rights of the
           -----------------
Banks and the Agent, that are expressed herein, shall be in addition to and not
in limitation of those provided by applicable law.

     6.6.  Severability. Whenever possible, each provision of this Amendment
           ------------
shall be interpreted in such manner as to be effective and valid under
applicable law; but if any provision of this Amendment shall be prohibited by or
invalid under applicable law, such provision shall be ineffective to the extent
of such prohibition or invalidity, without invalidating the remainder of such
provision or the remaining provisions of this Amendment.

     6.7.  No Forbearance. The Company acknowledges and agrees that the
           --------------
execution and delivery by the Agent and the Banks of this Amendment shall not be
deemed (i) to create a course of dealing or otherwise obligate the Agent or the
Banks to forbear or execute similar amendments under the same or similar
circumstances in the future, or (ii) to amend, relinquish or impair any right of
the Agent or the Banks to receive any indemnity or similar payment from any
Person or entity as a result of any matter arising from or relating to this
Amendment.

     6.8.  Successors and Assigns.  This Amendment shall be binding upon and
           ----------------------
inure to the benefit of the parties and thereto and their respective successors
and assigns.  No third party beneficiaries are intended in connection with this
Amendment.

     6.9.  Counterparts.  This Amendment may be executed in any number of
           ------------
counterparts, each of which shall be deemed an original, but all such
counterparts together shall constitute but one and the same instrument.  Each of
the parties hereto understands and agrees that this document (and any other
document required herein) may be delivered by any party thereto either in the
form of an executed original or an executed original sent by facsimile
transmission to be followed promptly by mailing of a hard copy original, and
that receipt by the Agent of a facsimile transmitted document purportedly
bearing the signature of a Bank or the Company shall bind such Bank or the
Company, respectively, with the same force and effect as the delivery of a hard
copy original.  Any failure by the Agent to receive the hard copy executed
original of such document shall not diminish the binding effect of receipt of
the facsimile transmitted executed original of such document of the party whose
hard copy page was not received by the Agent.

     6.10. Entire Agreement. This Amendment, together with the Credit Agreement,
           ----------------
contains the entire and exclusive agreement of the parties hereto with reference
to the matters discussed herein and therein. This Amendment supercedes all prior
drafts and communications with respect thereto. This Amendment may not be
amended except in accordance with the provisions of Section 12.1 of the Credit
Agreement.

     6.11. Officer's Certificate. In connection with the execution and delivery
           ---------------------
by the parties hereto of this Amendment, the Agent shall deliver to the Company
the Officer's Certificate substantially in the form attached hereto as Exhibit
A.

                                  *    *    *

                                      -6-
<PAGE>

          IN WITNESS WHEREOF, the parties hereto have caused the execution and
delivery hereof by their respective representatives thereunto duly authorized as
of the date first herein appearing.

                                   MATERIAL SCIENCES CORPORATION


                                   By: /s/ James J. Waclawik, Sr.
                                       ---------------------------
                                   Name:   James J. Waclawik, Sr.
                                        --------------------------
                                   Title:  Chief Financial Officer
                                         -------------------------

                                   BANK OF AMERICA, as Agent


                                   By: /s/ Kristine D. Hyde
                                       ---------------------------
                                   Name:   Kristine D. Hyde
                                        --------------------------
                                   Title:  Vice President - Senior
                                         -------------------------
                                           Agency Officer
                                         -------------------------

                                   BANK OF AMERICA, N.A., in its individual
                                   corporate capacity


                                   By: /s/ Chris D. Buckner
                                       ---------------------------
                                   Name:   Chris D. Buckner
                                        --------------------------
                                   Title:  Vice President
                                         -------------------------


                                   THE NORTHERN TRUST COMPANY


                                   By: /s/ Laurie A. Kieta
                                       ---------------------------
                                   Name:   Laurie A. Kieta
                                        --------------------------
                                   Title:  Vice President
                                         -------------------------

                                      -7-
<PAGE>

                           GUARANTOR ACKNOWLEDGMENT
                           ------------------------


     The undersigned, each a guarantor or third party pledgor with respect to
the Company's obligations to the Agent and the Banks under the Credit Agreement,
each hereby (i) acknowledge and consent to the execution, delivery and
performance by the Company of the foregoing Sixth Amendment to the Credit
Agreement ("Amendment"), and (ii) reaffirm and agree that the respective
            ---------
guaranty, third party pledge or security agreement to which the undersigned is
party and all other documents and agreements executed and delivered by the
undersigned to the Agent and the Banks in connection with the Credit Agreement
are in full force and effect, without defense, offset or counterclaim.
(Capitalized terms used herein have the meanings specified in the Amendment.)

                              GUARANTORS
                              ----------

                              MSC Pre Finish Metals Inc.
                              MSC Pre Finish Metals (EGV) Inc.
                              MSC Pre Finish Metals (MV) Inc.
                              MSC Pre Finish Metals (MT) Inc.
                              MSC Laminates and Composites Inc.
                              MSC Laminates and Composites (EGV) Inc.
                              MSC Walbridge Coatings Inc.
                              MSC Specialty Films, Inc*
                              MSC Pinole Point Steel Inc.
                              Solar-Gard International, Inc.*
                              MSC Pre Finish Metals (PP) Inc.
                              New SFI, LLC*


Dated as of June 21, 2001     By: /s/ James J. Waclawik, Sr.
                                  --------------------------
                              Title: Chief Financial Officer
                                     -----------------------


*  To be released from any applicable guaranty pursuant to the Sixth Amendment
concurrently with the MSC/SFI Closing.

                                      -8-
<PAGE>

                                   EXHIBIT A
                                   ---------

                             BANK OF AMERICA, N.A.

                             OFFICER'S CERTIFICATE
                             ---------------------


     In connection with that certain Sixth Amendment, Waiver and Consent (the
"Amendment"), dated as of June 21, 2001, by and among Material Sciences
 ---------
Corporation (the "Company"),  Bank of America, N.A., as agent, and the other
financial institutions party thereto, I, Chris Buckner, Vice President, of Bank
of America, N.A. (the "Bank"), DO HEREBY CERTIFY that:

     1.   The Bank has received the MSC/SFI Gross Cash Proceeds (as defined in
the Amendment) and applied such proceeds to the payment in full of the Revolving
Loans (as defined in the Amendment).

     2.   The conditions specified in Article V of the Amendment have been fully
satisfied.

     3.   After the date hereof, the only subsidiaries of the Company subject to
a guaranty pursuant to the Credit Agreement (as defined in the Amendment) are:


                           MSC Pre Finish Metals Inc.
                        MSC Pre Finish Metals (EGV) Inc.
                        MSC Pre Finish Metals (MV) Inc.
                        MSC Pre Finish Metals (MT) Inc.
                       MSC Laminates and Composites Inc.
                    MSC Laminates and Composites (EGV) Inc.
                          MSC Walbridge Coatings Inc.
                          MSC Pinole Point Steel Inc.
                        MSC Pre Finish Metals (PP) Inc.

     IN WITNESS WHEREOF, I have hereunto set my hand on behalf of the Bank this
__ day of June, 2001.



                                        BANK OF AMERICA, N.A.


                                         /s/ Chris D. Buckner
                                        ---------------------------
                                        By:  Chris D. Buckner
                                           ------------------------
                                        Its: Vice President
                                            -----------------------

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