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                                                                   Exhibit 10.6

                     CONTINUING LIMITED GUARANTY AGREEMENT
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                                   RECITALS
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     A. Zoltek Companies, Inc., a Missouri corporation, Zoltek Corporation, a
Missouri corporation, Engineering Technology Corporation, a Missouri
corporation and Zoltek Properties, Inc., a Missouri corporation (collectively,
"Borrower") is presently indebted or obligated to Southwest Bank of St. Louis
("Bank"), pursuant to that certain Standby Letter of Credit Application and
Agreement for Southwest Bank dated December 14, 2006, by and between Bank and
Borrower (the "Letter of Credit Reimbursement Agreement") relating to an
irrevocable standby letter of credit to be issued by Bank for the account of
Borrower and for the benefit of Travelers Casualty and Surety Company of
America, for itself and on behalf of its parents, affiliates and subsidiaries
in the original face amount of up to $40,000,000.00 (the "Letter of Credit");
and

     B. For the purpose of inducing Bank to issue the Letter of Credit
pursuant to the Letter of Credit Reimbursement Agreement, the undersigned
("Guarantor") agrees to guarantee the prompt payment of the indebtedness and
liabilities of Borrower to Bank under the Letter of Credit Reimbursement
Agreement in accordance with the terms and conditions hereinafter set forth.

                                  WITNESSETH
                                  ----------

     NOW, THEREFORE, for value received, and in consideration of the financial
accommodations given or to be given or continued to Borrower by Bank and/or of
Bank's presently refraining from making demand on Borrower or otherwise
pursuing Bank's legal remedies against Borrower, and for other good and
valuable consideration to Guarantor moving, the receipt and sufficiency of
which is hereby acknowledged:

     1. Guarantor hereby unconditionally guarantees to Bank the prompt payment
when due, whether by acceleration or otherwise, and at all times thereafter,
of any and all indebtedness and obligations of Borrower to Bank under the
Letter of Credit Reimbursement Agreement, including extensions, renewals or
refundings thereof (and extensions, renewals or refundings made after any
release or termination hereof), whether such be direct or indirect, liquidated
or unliquidated, absolute or contingent, single, joint, by the entirety or
several, now existing or hereafter arising, due or to become due (hereinafter
collectively referred to as "Liabilities" or, in the singular, "Liability").
"Liabilities" or a "Liability" shall also include reasonable expenses,
including reasonable attorney's fees, incurred by Bank in the efforts to
collect any Liability or to enforce the undertakings of Guarantor hereunder.
Whenever any such Liabilities shall become due and remain unpaid, Guarantor
will, on demand, make prompt payment of the amount due thereof; provided,
that, notwithstanding any provision contained herein to the contrary, while
the amount of the Liabilities that may be incurred by Borrower is not limited,
the liability of Guarantor to Bank hereunder shall not exceed Ten Million
Dollars ($10,000,000.00) plus the cost of enforcement of this Guaranty,
including court costs and reasonable attorneys' fees.

     2. Guarantor shall be obligated to make payment in full to Bank in
accordance with the terms and provisions hereof irrespective of the validity,
regularity or enforceability of any instrument or writing evidencing such
Liability or of the Liability itself, and if the Liability is secured, said
obligation of Guarantor to make payment hereunder shall be made irrespective
of the validity, perfection, regularity or enforceability of any instrument or
writing evidencing such security or of the security itself and it shall not be
necessary for Bank to resort to such security before enforcing Guarantor's
liability hereunder. Demand may be made upon Guarantor for the enforcement of
this Guaranty without the necessity of



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action at any time by Bank against Borrower or any collateral or to first
accelerate the maturity of any Liabilities. Any action taken by Bank against
Borrower, including foreclosure of any security held by Bank, shall in no
event be considered a waiver or diminishment of any rights against Guarantor
under this Guaranty and Bank shall, at its sole discretion, have the right at
any time to discontinue any action or proceeding against Borrower and require
full payment by Guarantor of the Liabilities together with attorneys' fees,
cost of the proceedings and court costs. It is agreed that a compromise and
settlement of any Liability shall, in no sense, compromise or settle
Guarantor's liability hereunder. Bank may apply any collateral for the
Liabilities in such order as it may elect and without any obligation to
account to Guarantor or any of them for the manner or order of application.

     3. Guarantor does hereby waive presentment of any instrument, demand for
payment, protest and notice of dishonor or nonpayment and, to the extent
permitted by applicable law, Guarantor waives all rights arising out of any
statute now existing or hereafter enacted with respect to guaranty or
suretyship and which may otherwise require Bank at any time to take legal
action against Borrower. Guarantor does hereby waive notice of the acceptance
of this Guaranty and notice of any Liability contracted or incurred by
Borrower.

     4. Bank may, from time to time, without the consent of or notice to
Guarantor, change the manner, interest rate, place or terms of payment, and
change or extend the time of payment of, refund, increase, decrease, renew or
alter in any manner any Liability or security therefor, and may, from time to
time, at its own discretion, without the consent of or notice to Guarantor,
exchange, release, surrender, realize upon or otherwise deal with in any
manner and in any order, any collateral pledged or mortgaged to secure any
Liability, without in any way affecting Guarantor's obligation hereunder.

     5. The obligations of Guarantor hereunder shall apply to all Liabilities,
including Liabilities arising on or prior to notice in writing from Guarantor
that Guarantor will not be responsible for any further Liabilities or notice
from Guarantor's personal representative that Guarantor has died or been
adjudicated incompetent. Any such notice, to be effective, must be actually
received by Bank. Notwithstanding the giving of such notice, the obligations
of Guarantor shall continue in full force and effect as to all Liabilities
then existing including those contingent, unliquidated or not yet accrued and
to any Liabilities thereafter arising, to the extent that Bank may be bound by
contract or otherwise to create or permit the creation of additional
Liabilities including those which may or might have been contingent,
unliquidated or not yet accrued Liabilities at the time such notice is given.

     6. Guarantor acknowledges and agrees that he has derived or will derive a
financial advantage from each and every loan, advance, or other extension of
credit and from each and every renewal, extension, modification, release of
collateral, or other relinquishment of legal rights made or granted or to be
granted by Bank to Borrower.

     7. This Guaranty shall be understood to be for the benefit of Bank or for
such other person or persons as may from time to time become or be the holders
of the Liabilities; and this Guaranty shall be transferable and negotiable
without notice to Guarantor with the same force and effect and to the same
extent as such Liabilities may be transferable.

     8. Guarantor agrees that Guarantor's liability hereunder is several and
independent of any other guaranties at any time in effect with respect to all
or any part of the Liabilities, and that Guarantor's liability hereunder may
be enforced regardless of the existence of any such other guaranty agreements.

     9. This Guaranty shall be binding upon Guarantor and upon Guarantor's
heirs, executors, personal representatives, administrators, legal
representatives, successors and assigns and shall likewise

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be enforceable against any trusts created by Guarantor and shall inure to the
benefit of Bank, its successors and assigns.

     10. This Guaranty shall not supersede any earlier guaranty of Guarantor
in which Bank has an interest, nor shall any later guaranty of Guarantor in
which Bank has an interest be construed to supersede this Guaranty. The effect
of any earlier, later or other guaranty shall be cumulative with this
Guaranty, whether or not the interests of Bank in such earlier, later or other
guaranty derives from arrangements made directly with Guarantor or indirectly
by way of Bank being a transferee of all or part of obligations of Borrower
guaranteed by Guarantor.

     11. Guarantor agrees that this Guaranty, and all obligations hereunder
shall remain in full force and effect at all times hereinafter during the term
hereof, notwithstanding any action or undertakings by, or against, Bank, or
concerning any collateral securing the Liabilities in any proceeding under any
bankruptcy law; including without limitation, matters relating to valuation of
collateral, election or imposition of secured or unsecured claim status upon
claims by Bank, pursuant to the Bankruptcy Code, or Rules of Bankruptcy
Procedure as may be applicable from time to time. Guarantor understands and
agrees that in the event any payment made by or on behalf of Borrower
respecting any Liability or any portion of any such payment shall at any time
be repaid by the recipient in compliance with an order (whether or not final)
by a court of competent jurisdiction pursuant to any provision of any
bankruptcy law as now existing or hereafter amended or applicable state law,
the Liabilities shall not be deemed to have been paid to the extent of the
repayment so made, the obligations of Guarantor shall continue in full force
and effect and such recipient, whether or not that be Bank, will continue to
be entitled to the full benefits of this Guaranty notwithstanding any release,
termination or return of this Guaranty. If acceleration of the time for
payment of any amount payable by Borrower to Bank is stayed upon the
insolvency, bankruptcy or reorganization of Borrower, all such amounts
otherwise subject to acceleration under the terms of the Liabilities shall
nonetheless be payable by Guarantor hereunder forthwith on demand by Bank.

     12. Bank shall have no obligation to inform Guarantor, and Guarantor
agrees to assume all responsibility for keeping informed as to Borrower's
financial condition, the possible non-payment and non-performance of the
Liabilities, and all matters relating to any collateral for the Liabilities or
for this Guaranty. At its option, Bank may, at any time, disclose information
concerning Borrower or any collateral for the Liabilities or this Guaranty,
but such disclosure shall not obligate Bank to provide the same information,
now or in the future, to Guarantor or additional information of any kind to
Guarantor.

     13. Guarantor hereby agrees that no payment by Guarantor of any Liability
shall entitle Guarantor by subrogation, indemnification, contribution,
reimbursement or otherwise to any payment by Borrower or by any other
guarantor of any Liability or from or out of any property of Borrower or of
any other guarantor of any Liability until all Liabilities have been paid in
full.

     14. Guarantor agrees to provide upon request of Bank financial statements
or such other information on Guarantor as Bank shall from time to time
reasonably request. In addition to the foregoing, Guarantor agrees that while
this Guaranty is in effect, Guarantor shall not permit, by any affirmative
action of Guarantor, a material adverse change in the liquidity or net worth
of Guarantor, nor shall Guarantor pledge or encumber in favor of any party
other than Bank any material assets of Guarantor; provided, however, that that
foregoing shall not apply to a pledge by the Guarantor of shares of Zoltek
Companies, Inc. common stock owned by the Guarantor as collateral for a loan
to Guarantor, the proceeds of which will loaned by Guarantor to the Borrowers.

     15. Notwithstanding anything to the contrary contained herein, and
provided that no draws have occurred under the Letter of Credit, Bank
acknowledges and agrees that this Guaranty shall be

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released in full upon (i) the receipt by Bank of the documents required under
the "Flood Insurance," "Survey" and "Appraisal" sections of that certain
Commitment Letter dated as of December 14, 2006 and issued by Bank to Zoltek
Corporation, provided that such documents are in form and substance reasonably
satisfactory to Bank, and (ii) the recordation of a Deed of Trust and Security
Agreement executed by Zoltek Properties, Inc. in favor of the Bank by which
Zoltek Properties, Inc. has granted to the Bank a lien upon the real property
owned by Zoltek Properties, Inc. and located at 1221 Fulwiler Road, Texas
79603, pursuant to which the Bank holds a second lien position in such real
property, in form and substance reasonably satisfactory to the Bank, subject
to matters of record; provided however, that Borrower shall use reasonable
efforts to insure or otherwise provide reasonable protection to Bank against
the mechanics lien recorded at Vol. 3143, page 732. In addition to the
foregoing, this Guaranty shall be released in full in the event that the Bank,
pursuant to Section 3(b) of that certain Third Amendment to Credit Agreement
            -----------
of even date herewith by and among the Borrower and the Bank, releases the
Bank's lien and security interest in the real property of any Borrower.

     16. This Guaranty shall be governed by and construed in accordance with
the laws of the State of Missouri without regard to conflict of laws
principles.

     17. Any indebtedness of Borrower for borrowed money now or hereafter owed
to Guarantor is hereby subordinated in right of payment to the payment of
amounts owing under this Guaranty as hereinafter set forth, any evidence of
such indebtedness shall be so marked with an appropriate legend and if a
default in the payment of any amounts then due and payable under this Guaranty
shall have occurred and be continuing, any such indebtedness of Borrower owed
to Guarantor, if collected or received by Guarantor, shall be held in trust by
Guarantor for Bank and be paid over to Bank for application in accordance with
this Guaranty.

     18. GUARANTOR HEREBY IRREVOCABLY SUBMITS TO THE JURISDICTION OF ANY STATE
OR FEDERAL COURT SITTING IN THE COUNTY OR CITY OF ST. LOUIS, MISSOURI OVER ANY
ACTION OR PROCEEDING ARISING OUT OF OR RELATING TO THIS GUARANTY, AND
GUARANTOR HEREBY IRREVOCABLY AGREES THAT ALL CLAIMS IN RESPECT TO SUCH ACTION
OR PROCEEDING MAY BE HEARD AND DETERMINED IN SUCH STATE OR FEDERAL COURT.
GUARANTOR HEREBY IRREVOCABLY WAIVES, TO THE FULLEST EXTENT IT MAY EFFECTIVELY
DO SO, THE DEFENSE OF AN INCONVENIENT FORUM TO THE MAINTENANCE OF SUCH ACTION
OR PROCEEDING. GUARANTOR AGREES THAT A FINAL JUDGMENT IN ANY SUCH ACTION OR
PROCEEDING SHALL BE CONCLUSIVE AND MAY BE ENFORCED IN OTHER JURISDICTIONS BY
SUIT ON THE JUDGMENT OR IN ANY OTHER MANNER PROVIDED BY LAW.

     19. The following notice is given pursuant to Section 432.047 of the
Missouri Revised Statutes; nothing contained in such notice shall be deemed to
limit or modify the terms of this Agreement. "ORAL AGREEMENTS OR COMMITMENTS
TO LOAN MONEY, EXTEND CREDIT OR TO FOREBEAR FROM ENFORCING REPAYMENT OF A DEBT
INCLUDING PROMISES TO EXTEND OR RENEW SUCH DEBT ARE NOT ENFORCEABLE REGARDLESS
OF THE LEGAL THEORY UPON WHICH IT IS BASED, THAT IS IN ANY WAY RELATED TO THE
CREDIT AGREEMENT. TO PROTECT YOU (GUARANTOR) AND US (CREDITOR) FROM
MISUNDERSTANDING OR DISAPPOINTMENT, ANY AGREEMENTS WE REACH COVERING SUCH
MATTERS ARE CONTAINED IN THIS WRITING, WHICH IS THE COMPLETE AND EXCLUSIVE
STATEMENT OF THE AGREEMENT BETWEEN US, EXCEPT AS WE MAY LATER AGREE IN WRITING
TO MODIFY IT."

     20. GUARANTOR HEREBY WAIVES ANY RIGHT TO TRIAL BY JURY (WHICH BANK ALSO
WAIVES) IN ANY ACTION, SUIT, PROCEEDING OR COUNTERCLAIM OF ANY KIND ARISING
OUT OF OR RELATING TO THIS GUARANTY, ANY LIABILITIES OR BANK'S CONDUCT IN
RESPECT TO ANY OF THE FOREGOING.


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     IN WITNESS WHEREOF, this instrument has been duly executed by Guarantor
this 21st day of December, 2006.


                                  /s/ Zsolt Rumy
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                                  Zsolt Rumy

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