<PAGE>

                                                                 Exhibit 4.6

                                                                   EXHIBIT B
                                                                   ---------

                        REGISTRATION RIGHTS AGREEMENT

                  This Registration Rights Agreement (this "AGREEMENT") is
made and entered into as of October 14, 2004, by and among Zoltek Companies,
Inc., a Missouri corporation (the "COMPANY"), and the investors signatory
hereto (each a "INVESTOR" and collectively, the "INVESTORS").

                  This Agreement is made pursuant to the Loan and Warrant
Agreement, dated as of October 14, 2004, among the Company and the Investors
(the "PURCHASE AGREEMENT").

                  The Company and the Investors hereby agree as follows:

         1.       Definitions. Capitalized terms used and not otherwise defined
                  -----------
herein that are defined in the Purchase Agreement shall have the meanings
given such terms in the Purchase Agreement. As used in this Agreement, the
following terms shall have the respective meanings set forth in this Section 1:

                  "EFFECTIVE DATE" means the date that the Registration
Statement filed pursuant to Section 2(a) is first declared effective by the
Commission.

                  "EFFECTIVENESS DATE" means: (a) with respect to the
initial Registration Statement required to be filed to cover the resale by
the Holders of the Registrable Securities, the earlier of: (a)(i) the 90th
day following the Closing Date; provided, that, if the Commission reviews
                                --------
and has written comments to the filed Registration Statement that would
require the filing of a pre-effective amendment thereto with the Commission,
then the Effectiveness Date under this clause (a)(i) shall be the 120th day
following the Closing Date, and (ii) the fifth Trading Day following the
date on which the Company is notified by the Commission that the initial
Registration Statement will not be reviewed or is no longer subject to
further review and comments, and (b) with respect to any additional
Registration Statements that may be required pursuant to Section 2(b)
hereof, the earlier of: (i) the 90th day following the date on which the
Company first knows, or reasonably should have known, that such additional
Registration Statement is required under such Section; provided, that, if
                                                       --------
the Commission reviews and has written comments to such filed Registration
Statement that would require the filing of a pre-effective amendment thereto
with the Commission, then the Effectiveness Date under this clause (b)(i)
shall be the 120th day following the date that the Company first knows, or
reasonably should have known, that such additional Registration Statement is
required under such Section, and (ii) the fifth Trading Day following the
date on which the Company is notified by the Commission that such additional
Registration Statement will not be reviewed or is no longer subject to
further review and comments.

                  "EFFECTIVENESS PERIOD" shall have the meaning set forth in
Section 2(a).

                                    -1-

                  "EXCHANGE ACT" means the Securities Exchange Act of 1934,
as amended.

                  "FILING DATE" means: (a) with respect to the initial
Registration Statement required to be filed to cover the resale by the
Holders of the Registrable Securities, the 30th day following the Closing
Date, and (b) with respect to any additional Registration Statements that
may be required pursuant to Section 2(b) hereof, the 30th day following the
date on which the Company first knows, or reasonably should have known, that
such additional Registration Statement is required under such Section.

                  "HOLDER" or "HOLDERS" means the holder or holders, as the
case may be, from time to time of Registrable Securities.

                  "INDEMNIFIED PARTY" shall have the meaning set forth in
Section 5(c).

                  "INDEMNIFYING PARTY" shall have the meaning set forth in
Section 5(c).

                  "LOSSES" shall have the meaning set forth in Section 5(a).

                  "NOTES" means, collectively, each of the senior secured
convertible promissory notes, due on the date that is 42 months after the
Closing Date, each issuable by the Company to one of the Lenders (as defined
in the Purchase Agreement) pursuant to the Purchase Agreement.

                  "PROCEEDING" means an action, claim, suit, investigation
or proceeding (including, without limitation, an investigation or partial
proceeding, such as a deposition), whether commenced or threatened.

                  "PROSPECTUS" means the prospectus included in a
Registration Statement (including, without limitation, a prospectus that
includes any information previously omitted from a prospectus filed as part
of an effective registration statement in reliance upon Rule 430A
promulgated under the Securities Act), as amended or supplemented by any
prospectus supplement, with respect to the terms of the offering of any
portion of the Registrable Securities covered by a Registration Statement,
and all other amendments and supplements to the Prospectus, including
post-effective amendments, and all material incorporated by reference or
deemed to be incorporated by reference in such Prospectus.

                  "REGISTRABLE SECURITIES" means the Underlying Shares
issuable upon (a) conversion of the Notes (assuming such Notes are held
until the maturity date thereof and all interest is accreted to principal
thereunder), and (b) upon exercise of the Warrants, together in each case of
(a) and (b) above with any securities issued or issuable upon any stock
split, dividend or other distribution, recapitalization or similar event, or
any conversion price adjustment with respect thereto.

                  "REGISTRATION STATEMENT" means each of the following: (i)
an initial registration statement which is required to register the resale
of the Registrable Securities, (ii) each additional registration statement,
if any, contemplated by Section 2(b), and including, in each case, the
Prospectus, amendments and supplements to each such



                                    -2-

registration statement or Prospectus, including pre- and post-effective
amendments, all exhibits thereto, and all material incorporated by reference
or deemed to be incorporated by reference in such registration statement.

                  "RULE 144" means Rule 144 promulgated by the Commission
pursuant to the Securities Act, as such Rule may be amended from time to
time, or any similar rule or regulation hereafter adopted by the Commission
having substantially the same effect as such Rule.

                  "RULE 415" means Rule 415 promulgated by the Commission
pursuant to the Securities Act, as such Rule may be amended from time to
time, or any similar rule or regulation hereafter adopted by the Commission
having substantially the same effect as such Rule.

                  "RULE 424" means Rule 424 promulgated by the Commission
pursuant to the Securities Act, as such Rule may be amended from time to
time, or any similar rule or regulation hereafter adopted by the Commission
having substantially the same effect as such Rule.

                  "SECURITIES ACT" means the Securities Act of 1933, as
amended.

                  "WARRANTS" has the meaning ascribed in the Purchase
Agreement.

         2.       Registration.
                  ------------

                  (a) On or prior to each Filing Date, the Company shall
prepare and file with the Commission a Registration Statement covering the
resale of all Registrable Securities not already covered by an existing and
effective Registration Statement for an offering to be made on a continuous
basis pursuant to Rule 415. The Registration Statement shall be on Form S-3
(except if the Company is not then eligible to register for resale the
Registrable Securities on Form S-3, in which case such registration shall be
on another appropriate form for such purpose) and shall contain (except if
otherwise required pursuant to written comments received from the Commission
upon a review of such Registration Statement) the "Plan of Distribution"
substantially in the form attached hereto as Annex A. The Company shall
                                             -------
cause each Registration Statement to be declared effective under the
Securities Act as soon as possible but, in any event, no later than its
Effectiveness Date, and shall use its best efforts to keep each Registration
Statement continuously effective under the Securities Act until the sixth
year after the date that the Registration Statement is declared effective by
the Commission or such earlier date when all Registrable Securities covered
by the Registration Statement have been sold or may be sold without volume
restrictions pursuant to Rule 144(k) as determined by the counsel to the
Company pursuant to a written opinion letter to such effect, addressed and
acceptable to the Company's transfer agent and the affected Holders (the
"EFFECTIVENESS PERIOD"). The initial Registration Statement shall include a
number of Registrable Securities equal to the sum of (a) the number of
Underlying Shares issuable upon an assumed conversion in full of the Notes
(assuming for such purpose that the Conversion Price is 75% of the
conversion price on the Closing Date, the Notes are held until their full
Maturity Dates


                                    -3-

and all interest accretes to principal for the life thereof), and (b) the
number of Underlying Shares issuable upon a conversion in full of the
Warrants (assuming for such purpose that the exercise price of the Warrants
is 75% of the exercise price on the Closing Date, as such sum may be
required to be reduced pursuant to written comments to the Registration
Statement received from the Commission.

                  (b) If for any reason the Commission does not permit all of
the Registrable Securities to be included in the Registration Statement
filed pursuant to Section 2(a) or for any other reason all Registrable
Securities then outstanding are not then included in an effective
Registration Statement, then the Company shall prepare and file as soon as
possible after the date on which the Commission shall indicate as being the
first date or time that such filing may be made, but in any event by the
30th day following such date, an additional Registration Statement covering
the resale of all Registrable Securities not already covered by an existing
and effective Registration Statement for an offering to be made on a
continuous basis pursuant to Rule 415, on Form S-3 (except if the Company is
not then eligible to register for resale the Registrable Securities on Form
S-3, in which case such registration shall be on another appropriate form
for such purpose). Each such Registration Statement shall contain (except if
otherwise required pursuant to written comments received from the Commission
upon a review of such Registration Statement) the "Plan of Distribution"
attached hereto as Annex A. The Company shall cause each such Registration
                   -------
Statement to be declared effective under the Securities Act as soon as
possible but, in any event, no later than the 90th day following the date on
which the Company becomes aware that such Registration Statement is required
to be filed under this Agreement, and shall use its best efforts to keep
such Registration Statement continuously effective under the Securities Act
during the entire Effectiveness Period.

                  (c) If: (i) a Registration Statement is not filed on or
prior to its Filing Date (if the Company files a Registration Statement
without affording the Holders the opportunity to review and comment on the
same as required by Section 3(a) hereof, the Company shall not be deemed to
have satisfied this clause (i)), or (ii) a Registration Statement is not
declared effective by the Commission on or prior to its required
Effectiveness Date, or (iii) after the Effective Date, such Registration
Statement ceases for any reason to be effective or the prospectus thereunder
ceases to available to the Holders as to all Registrable Securities to which
it is required to cover at any time prior to the expiration of its
Effectiveness Period for an aggregate of more than an aggregate of 20
Trading Days (which need not be consecutive, (any such failure or breach
being referred to as an "EVENT," and for purposes of clauses (i) or (ii) the
date on which such Event occurs, or for purposes of clause (iii) the date
which such 20 Trading Day-period is exceeded, being referred to as "EVENT
DATE"), then, in addition to any other rights available to the Holders under
the Transaction Documents or under applicable law: (x) on each such Event
Date and on each monthly anniversary of each such Event Date thereof (if the
applicable Event shall not have been cured by such date) until the
applicable Event is cured, the Company shall pay to each Holder an amount in
cash, as liquidated damages and not as a penalty, equal to 1.5% of the
aggregate Loan Amount loaned by such Holder pursuant to the Purchase
Agreement. If the Company fails to pay any liquidated damages pursuant to
this Section in full within seven days after the date payable, the Company
will


                                    -4-

pay interest thereon at a rate of 12% per annum (or such lesser maximum
amount that is permitted to be paid by applicable law) to the Holder,
accruing daily from the date such liquidated damages are due until such
amounts, plus all such interest thereon, are paid in full. The liquidated
damages pursuant to the terms hereof shall apply on a pro rata basis for any
portion of a month prior to the cure of an Event.

         3.       Registration Procedures.
                  -----------------------

                  In connection with the Company's registration obligations
hereunder, the Company shall:

                  (a) Not less than four Trading Days prior to the filing of
a Registration Statement or any related Prospectus or any amendment or
supplement thereto, the Company shall furnish to the Holders copies of all
such documents proposed to be filed which documents (other than those
incorporated by reference) will be subject to the review of such Holders.
The Company shall not file a Registration Statement or any such Prospectus
or any amendments or supplements thereto to which the Holders of a majority
of the Registrable Securities shall reasonably object in good faith.

                  (b) (i) Prepare and file with the Commission such
amendments, including post-effective amendments, to each Registration
Statement and the Prospectus used in connection therewith as may be
necessary to keep such Registration Statement continuously effective as to
the applicable Registrable Securities for its Effectiveness Period and
prepare and file with the Commission such additional Registration Statements
in order to register for resale under the Securities Act all of the
Registrable Securities; (ii) cause the related Prospectus to be amended or
supplemented by any required Prospectus supplement, and as so supplemented
or amended to be filed pursuant to Rule 424; (iii) respond as promptly as
reasonably possible to any comments received from the Commission with
respect to each Registration Statement or any amendment thereto and, as
promptly as reasonably possible provide the Holders true and complete copies
of all correspondence from and to the Commission relating to such
Registration Statement that would not result in the disclosure to the
Holders of material and non-public information concerning the Company; and
(iv) comply in all material respects with the provisions of the Securities
Act and the Exchange Act with respect to the Registration Statements and the
disposition of all Registrable Securities covered by each Registration
Statement.

                  (c) Notify the Holders as promptly as reasonably possible
(and, in the case of (i)(A) below, not less than three Trading Days prior to
such filing) and (if requested by any such Person) confirm such notice in
writing no later than one Trading Day following the day (i)(A) when a
Prospectus or any Prospectus supplement or post-effective amendment to a
Registration Statement is proposed to be filed; (B) when the Commission
notifies the Company whether there will be a "review" of such Registration
Statement and whenever the Commission comments in writing on such
Registration Statement (the Company shall provide true and complete copies
of any such comments all written responses thereto to each Holder that
pertains to such Holder as a Selling Shareholder or to the Plan of
Distribution, but not information which the


                                    -5-

Company believes would constitute material and non-public information); and
(C) with respect to each Registration Statement or any post-effective
amendment, when the same has become effective; (ii) of any request by the
Commission or any other Federal or state governmental authority for
amendments or supplements to a Registration Statement or Prospectus or for
additional information; (iii) of the issuance by the Commission of any stop
order suspending the effectiveness of a Registration Statement covering any
or all of the Registrable Securities or the initiation of any Proceedings
for that purpose; (iv) of the receipt by the Company of any notification
with respect to the suspension of the qualification or exemption from
qualification of any of the Registrable Securities for sale in any
jurisdiction, or the initiation or threatening of any Proceeding for such
purpose; and (v) of the occurrence of any event or passage of time that
makes the financial statements included in a Registration Statement
ineligible for inclusion therein or any statement made in such Registration
Statement or Prospectus or any document incorporated or deemed to be
incorporated therein by reference untrue in any material respect or that
requires any revisions to such Registration Statement, Prospectus or other
documents so that, in the case of such Registration Statement or the
Prospectus, as the case may be, it will not contain any untrue statement of
a material fact or omit to state any material fact required to be stated
therein or necessary to make the statements therein, in light of the
circumstances under which they were made, not misleading.

                  (d) Use its best efforts to avoid the issuance of, or, if
issued, obtain the withdrawal of (i) any order suspending the effectiveness
of a Registration Statement, or (ii) any suspension of the qualification (or
exemption from qualification) of any of the Registrable Securities for sale
in any jurisdiction, at the earliest practicable moment.

                  (e) Furnish to each Holder, without charge, at least one
conformed copy of each Registration Statement and each amendment thereto and
all exhibits to the extent requested by such Person (excluding those
previously furnished or incorporated by reference) promptly after the filing
of such documents with the Commission.

                  (f) Promptly deliver to each Holder, without charge, as
many copies of each Prospectus or Prospectuses (including each form of
prospectus) and each amendment or supplement thereto as such Persons may
reasonably request. The Company hereby consents to the use of such
Prospectus and each amendment or supplement thereto by each of the selling
Holders in connection with the offering and sale of the Registrable
Securities covered by such Prospectus and any amendment or supplement
thereto.

                  (g) Prior to any public offering of Registrable
Securities, use its best efforts to register or qualify or cooperate with
the selling Holders in connection with the registration or qualification (or
exemption from such registration or qualification) of such Registrable
Securities for offer and sale under the securities or Blue Sky laws of all
jurisdictions within the United States, to keep each such registration or
qualification (or exemption therefrom) effective during the Effectiveness
Period and to do any and all other acts or things necessary or advisable to
enable the disposition in such jurisdictions of the Registrable Securities
covered by the Registration Statements; provided, that the Company shall not
                                        --------
be required to qualify generally to do business in any jurisdiction


                                    -6-

where it is not then so qualified or subject the Company to any material tax
in any such jurisdiction where it is not then so subject.

                  (h) Cooperate with the Holders to facilitate the timely
preparation and delivery of certificates representing Registrable Securities
to be delivered to a transferee pursuant to the Registration Statements,
which certificates shall be free, to the extent permitted by the Purchase
Agreement, of all restrictive legends, and to enable such Registrable
Securities to be in such denominations and registered in such names as any
such Holders may request.

                  (i) Upon the occurrence of any event contemplated by
Section 3(c)(v), as promptly as reasonably possible, prepare a supplement or
amendment, including a post-effective amendment, to the affected
Registration Statements or a supplement to the related Prospectus or any
document incorporated or deemed to be incorporated therein by reference, and
file any other required document so that, as thereafter delivered, no
Registration Statement nor any Prospectus will contain an untrue statement
of a material fact or omit to state a material fact required to be stated
therein or necessary to make the statements therein, in light of the
circumstances under which they were made, not misleading.

                  (j) The Company may require each selling Holder to furnish
to the Company a certified statement as to the number of shares of Common
Stock beneficially owned by such Holder and, if requested by the Commission,
the controlling person thereof.

                  (k) The Company has read and understands the conversion
and exercise limitations contained in the Notes and the Warrants and will
not take a position in any Registration Statement or other filing with the
Commission that a Holder is the beneficial owner of more than the percentage
of Common Stock permitted to be beneficially owned by such Holder absent an
affirmative written statement by such Holder to such effect.

         4.       Registration Expenses. All fees and expenses incident to
                  ---------------------
the performance of or compliance with this Agreement by the Company shall be
borne by the Company whether or not any Registrable Securities are sold
pursuant to a Registration Statement. The fees and expenses referred to in
the foregoing sentence shall include, without limitation, (i) all
registration and filing fees (including, without limitation, fees and
expenses (A) with respect to filings required to be made with any Trading
Market on which the Common Stock is then listed for trading, and (B) in
compliance with applicable state securities or Blue Sky laws), (ii) printing
expenses (including, without limitation, expenses of printing certificates
for Registrable Securities and of printing prospectuses if the printing of
prospectuses is reasonably requested by the holders of a majority of the
Registrable Securities included in the Registration Statement), (iii)
messenger, telephone and delivery expenses, (iv) fees and disbursements of
counsel for the Company, (v) Securities Act liability insurance, if the
Company so desires such insurance, and (vi) fees and expenses of all other
Persons retained by the Company in connection with the consummation of the
transactions contemplated by this Agreement.


                                    -7-

In addition, the Company shall be responsible for all of its internal
expenses incurred in connection with the consummation of the transactions
contemplated by this Agreement (including, without limitation, all salaries
and expenses of its officers and employees performing legal or accounting
duties), the expense of any annual audit and the fees and expenses incurred
in connection with the listing of the Registrable Securities on any
securities exchange as required hereunder.

         5.       Indemnification.
                  ---------------

                  (a) Indemnification by the Company. The Company shall,
                      ------------------------------
notwithstanding any termination of this Agreement, indemnify and hold
harmless each Holder, the officers, directors, agents, investment advisors,
partners, members, shareholders and employees of each of them, each Person
who controls any such Holder (within the meaning of Section 15 of the
Securities Act or Section 20 of the Exchange Act) and the officers,
directors, agents and employees of each such controlling Person, to the
fullest extent permitted by applicable law, from and against any and all
losses, claims, damages, liabilities, costs (including, without limitation,
reasonable costs of preparation and reasonable attorneys' fees) and expenses
(collectively, "LOSSES"), as incurred, arising out of or relating to any
untrue or alleged untrue statement of a material fact contained in any
Registration Statement, any Prospectus or any form of prospectus or in any
amendment or supplement thereto or in any preliminary prospectus, or arising
out of or relating to any omission or alleged omission of a material fact
required to be stated therein or necessary to make the statements therein
(in the case of any Prospectus or form of prospectus or supplement thereto,
in light of the circumstances under which they were made) not misleading,
except to the extent, but only to the extent, that (1) such untrue
statements or omissions are based solely upon information regarding such
Holder furnished in writing to the Company by such Holder expressly for use
therein, or to the extent that such information relates to such Holder or
such Holder's proposed method of distribution of Registrable Securities and
was reviewed and expressly approved in writing by such Holder expressly for
use in the Registration Statement, such Prospectus or such form of
Prospectus or in any amendment or supplement thereto (it being understood
that the Holder has approved Annex A hereto for this purpose) or (2) in the
case of an occurrence of an event of the type specified in Section
3(c)(ii)-(v), the use by such Holder of an outdated or defective Prospectus
after the Company has notified such Holder in writing that the Prospectus is
outdated or defective and prior to the receipt by such Holder of an Advice
or an amended or supplemented Prospectus, but only if and to the extent that
following the receipt of the Advice or the amended or supplemented
Prospectus the misstatement or omission giving rise to such Loss would have
been corrected. The Company shall notify the Holders promptly of the
institution, threat or assertion of any Proceeding of which the Company is
aware in connection with the transactions contemplated by this Agreement.

                  (b) Indemnification by Holders. Each Holder shall,
                      --------------------------
severally and not jointly, indemnify and hold harmless the Company, its
directors, officers, agents and employees, each Person who controls the
Company (within the meaning of Section 15 of the Securities Act and Section
20 of the Exchange Act), and the directors, officers, agents or employees of
such controlling Persons, to the fullest extent permitted by applicable


                                    -8-

law, from and against all Losses, as incurred, arising solely out of or based
solely upon: (x) such Holder's failure to comply with the prospectus
delivery requirements of the Securities Act or (y) any untrue statement of a
material fact contained in any Registration Statement, any Prospectus, or
any form of prospectus, or in any amendment or supplement thereto, or
arising solely out of or based solely upon any omission of a material fact
required to be stated therein or necessary to make the statements therein
not misleading to the extent, but only to the extent that, (1) such untrue
statements or omissions are based solely upon information regarding such
Holder furnished in writing to the Company by such Holder expressly for use
therein, or to the extent that such information relates to such Holder or
such Holder's proposed method of distribution of Registrable Securities and
was reviewed and expressly approved in writing by such Holder expressly for
use in the Registration Statement (it being understood that the Holder has
approved Annex A hereto for this purpose), such Prospectus or such form of
Prospectus or in any amendment or supplement thereto or (2) in the case of
an occurrence of an event of the type specified in Section 3(c)(ii)-(v), the
use by such Holder of an outdated or defective Prospectus after the Company
has notified such Holder in writing that the Prospectus is outdated or
defective and prior to the receipt by such Holder of an Advice or an amended
or supplemented Prospectus, but only if and to the extent that following the
receipt of the Advice or the amended or supplemented Prospectus the
misstatement or omission giving rise to such Loss would have been corrected.
In no event shall the liability of any selling Holder hereunder be greater
in amount than the dollar amount of the net proceeds received by such Holder
upon the sale of the Registrable Securities giving rise to such
indemnification obligation.

                  (c) Conduct of Indemnification Proceedings. If any
                      --------------------------------------
Proceeding shall be brought or asserted against any Person entitled to
indemnity hereunder (an "INDEMNIFIED PARTY"), such Indemnified Party shall
promptly notify the Person from whom indemnity is sought (the "INDEMNIFYING
PARTY") in writing, and the Indemnifying Party shall assume the defense
thereof, including the employment of counsel reasonably satisfactory to the
Indemnified Party and the payment of all fees and expenses incurred in
connection with defense thereof; provided, that the failure of any
Indemnified Party to give such notice shall not relieve the Indemnifying
Party of its obligations or liabilities pursuant to this Agreement, except
(and only) to the extent that it shall be finally determined by a court of
competent jurisdiction (which determination is not subject to appeal or
further review) that such failure shall have proximately and materially
adversely prejudiced the Indemnifying Party.

                  An Indemnified Party shall have the right to employ
separate counsel in any such Proceeding and to participate in the defense
thereof, but the fees and expenses of such counsel shall be at the expense
of such Indemnified Party or Parties unless: (1) the Indemnifying Party has
agreed in writing to pay such fees and expenses; (2) the Indemnifying Party
shall have failed promptly to assume the defense of such Proceeding and to
employ counsel reasonably satisfactory to such Indemnified Party in any such
Proceeding; or (3) the named parties to any such Proceeding (including any
impleaded parties) include both such Indemnified Party and the Indemnifying
Party, and such Indemnified Party shall have been advised by counsel that a
conflict of interest is likely to exist if the same counsel were to
represent such Indemnified Party and the


                                    -9-

Indemnifying Party (in which case, if such Indemnified Party notifies the
Indemnifying Party in writing that it elects to employ separate counsel at
the expense of the Indemnifying Party, the Indemnifying Party shall not have
the right to assume the defense thereof and such counsel shall be at the
expense of the Indemnifying Party). The Indemnifying Party shall not be
liable for any settlement of any such Proceeding effected without its
written consent, which consent shall not be unreasonably withheld. No
Indemnifying Party shall, without the prior written consent of the
Indemnified Party, effect any settlement of any pending Proceeding in
respect of which any Indemnified Party is a party, unless such settlement
includes an unconditional release of such Indemnified Party from all
liability on claims that are the subject matter of such Proceeding.

                  All reasonable fees and expenses of the Indemnified Party
(including reasonable fees and expenses to the extent incurred in connection
with investigating or preparing to defend such Proceeding in a manner not
inconsistent with this Section) shall be paid to the Indemnified Party, as
incurred, within ten Trading Days of written notice thereof to the
Indemnifying Party (regardless of whether it is ultimately determined that
an Indemnified Party is not entitled to indemnification hereunder; provided,
that the Indemnifying Party may require such Indemnified Party to undertake
to reimburse all such fees and expenses to the extent it is finally
judicially determined that such Indemnified Party is not entitled to
indemnification hereunder).

                  (d) Contribution. If a claim for indemnification under
                      ------------
Section 5(a) or 5(b) is unavailable to an Indemnified Party (by reason of
public policy or otherwise), then each Indemnifying Party, in lieu of
indemnifying such Indemnified Party, shall contribute to the amount paid or
payable by such Indemnified Party as a result of such Losses, in such
proportion as is appropriate to reflect the relative fault of the
Indemnifying Party and Indemnified Party in connection with the actions,
statements or omissions that resulted in such Losses as well as any other
relevant equitable considerations. The relative fault of such Indemnifying
Party and Indemnified Party shall be determined by reference to, among other
things, whether any action in question, including any untrue or alleged
untrue statement of a material fact or omission or alleged omission of a
material fact, has been taken or made by, or relates to information supplied
by, such Indemnifying Party or Indemnified Party, and the parties' relative
intent, knowledge, access to information and opportunity to correct or
prevent such action, statement or omission. The amount paid or payable by a
party as a result of any Losses shall be deemed to include, subject to the
limitations set forth in Section 5(c), any reasonable attorneys' or other
reasonable fees or expenses incurred by such party in connection with any
Proceeding to the extent such party would have been indemnified for such
fees or expenses if the indemnification provided for in this Section was
available to such party in accordance with its terms.

                  The parties hereto agree that it would not be just and
equitable if contribution pursuant to this Section 5(d) were determined by
pro rata allocation or by any other method of allocation that does not take
into account the equitable considerations referred to in the immediately
preceding paragraph. Notwithstanding the provisions of this Section 5(d), no
Holder shall be required to contribute, in the


                                    -10-

aggregate, any amount in excess of the amount by which the proceeds actually
received by such Holder from the sale of the Registrable Securities subject
to the Proceeding exceeds the amount of any damages that such Holder has
otherwise been required to pay by reason of such untrue or alleged untrue
statement or omission or alleged omission.

                  The indemnity and contribution agreements contained in
this Section are in addition to any liability that the Indemnifying Parties
may have to the Indemnified Parties.

         6.       Miscellaneous
                  -------------

                  (a) Remedies. In the event of a breach by the Company or
                      --------
by a Holder, of any of their obligations under this Agreement, each Holder
or the Company, as the case may be, in addition to being entitled to
exercise all rights granted by law and under this Agreement, including
recovery of damages, will be entitled to specific performance of its rights
under this Agreement. The Company and each Holder agree that monetary
damages would not provide adequate compensation for any losses incurred by
reason of a breach by it of any of the provisions of this Agreement and
hereby further agrees that, in the event of any action for specific
performance in respect of such breach, it shall waive the defense that a
remedy at law would be adequate.

                  (b) No Piggyback on Registrations. Except as and to the
                      -----------------------------
extent specified in Schedule 6(b) hereto, neither the Company nor any of its
                    -------------
security holders (other than the Holders in such capacity pursuant hereto)
may include securities of the Company in a Registration Statement other than
the Registrable Securities, and the Company shall not after the date hereof
enter into any agreement providing any such right to any of its security
holders. Except as and to the extent specified in Schedule 3.1(g) of the
                                                  ---------------
Purchase Agreement, the Company has not previously entered into any
agreement granting any registration rights with respect to any of its
securities to any Person which have not been fully satisfied.

                  (c) Compliance. Each Holder covenants and agrees that it
                      ----------
will comply with the prospectus delivery requirements of the Securities Act
as applicable to it in connection with sales of Registrable Securities
pursuant to the Registration Statement.

                  (d) Discontinued Disposition. Each Holder agrees by its
                      ------------------------
acquisition of such Registrable Securities that, upon receipt of a notice
from the Company of the occurrence of any event of the kind described in
Section 3(c), such Holder will forthwith discontinue disposition of such
Registrable Securities under the Registration Statement until such Holder's
receipt of the copies of the supplemented Prospectus and/or amended
Registration Statement or until it is advised in writing (the "ADVICE") by
the Company that the use of the applicable Prospectus may be resumed, and,
in either case, has received copies of any additional or supplemental
filings that are incorporated or deemed to be incorporated by reference in
such Prospectus or Registration Statement. The Company may provide
appropriate stop orders to enforce the provisions of this paragraph.

                                    -11-

                  (e) Piggy-Back Registrations. If at any time during the
                      ------------------------
Effectiveness Period there is not an effective Registration Statement
covering all of the Registrable Securities and the Company shall determine
to prepare and file with the Commission a registration statement relating to
an offering for its own account or the account of others under the
Securities Act of any of its equity securities, other than on Form S-4 or
Form S-8 (each as promulgated under the Securities Act) or their then
equivalents relating to equity securities to be issued solely in connection
with any acquisition of any entity or business or equity securities issuable
in connection with stock option or other employee benefit plans, then the
Company shall send to each Holder written notice of such determination and,
if within fifteen days after receipt of such notice, any such Holder shall
so request in writing, the Company shall include in such registration
statement all or any part of such Registrable Securities such holder
requests to be registered, subject to customary underwriter cutbacks
applicable to all holders of registration rights. In connection with each
such registration covering an underwritten public offering, (i) the Company
shall select the investment banker(s) and manager(s) (which shall be
nationally recognized) for such offering and (ii) the Holder agrees to enter
into a written agreement with the managing underwriter selected in the
manner herein provided in such form and containing such provisions as are
customary in the securities business for such an arrangement between such
underwriter and selling shareholders, provided, that the Holders shall not
be obligated to refrain or "lock up" from selling any Registrable Securities
or other securities of the Company for any period of time.

                  (f) Amendments and Waivers. The provisions of this
                      ----------------------
Agreement, including the provisions of this sentence, may not be amended,
modified or supplemented, and waivers or consents to departures from the
provisions hereof may not be given, unless the same shall be in writing and
signed by the Company and the Holders of all of the then outstanding
Registrable Securities. Notwithstanding the foregoing, a waiver or consent
to depart from the provisions hereof with respect to a matter that relates
exclusively to the rights of certain Holders and that does not directly or
indirectly affect the rights of other Holders may be given by Holders of at
least 66 2/3% of the Registrable Securities to which such waiver or consent
relates, provided, that the provisions of this sentence may not be amended,
         --------
modified, or supplemented except in accordance with the provisions of the
immediately preceding sentence.

                  (g) Notices. Any and all notices or other communications
                      -------
or deliveries required or permitted to be provided hereunder shall be in
writing and shall be deemed given and effective on the earliest of (i) the
date of transmission, if such notice or communication is delivered via
facsimile at the facsimile telephone number specified in this Section prior
to 6:30 p.m. (New York City time) on a Trading Day, (ii) the Trading Day
after the date of transmission, if such notice or communication is delivered
via facsimile at the facsimile telephone number specified in this Agreement
later than 6:30 p.m. (New York City time) on any date and earlier than 11:59
p.m. (New York City time) on such date, (iii) the Trading Day following the
date of mailing, if sent by nationally recognized overnight courier service,
or (iv) upon actual receipt by the party to whom such notice is required to
be given. The address for such notices and communications shall be as
follows:

                                    -12-


         If to the Company:         Zoltek Companies, Inc.
                                    3101 McKelvey Road
                                    St. Louis, Missouri 63044
                                    Facsimile No.: (314) 291-9082
                                    Attn: Chief Financial Officer

                                    With a copy to:

                                    Thompson Coburn LLP
                                    One US Bank Plaza
                                    St. Louis, Missouri 63101
                                    Facsimile No.: (314) 552-7000
                                    Attn: Thomas A. Litz, Esq.


         If to a Investor:          To the address set forth under such
                                    Investor's name on the signature pages
                                    hereto.

         If to any other Person who is then the registered Holder:

                                    To the address of such Holder as it
                                    appears in the stock transfer books of
                                    the Company

or such other address as may be designated in writing hereafter, in the same
manner, by such Person.

                  (h) Successors and Assigns. This Agreement shall inure to
                      ----------------------
the benefit of and be binding upon the successors and permitted assigns of
each of the parties and shall inure to the benefit of each Holder. The
Company may not assign its rights or obligations hereunder without the prior
written consent of each Holder. Each Holder may assign its respective rights
hereunder in the manner and to the Persons as permitted under the Purchase
Agreement so long as such assignment complies with the Purchaser Agreement.

                  (i) Execution and Counterparts. This Agreement may be
                      --------------------------
executed in any number of counterparts, each of which when so executed shall
be deemed to be an original and, all of which taken together shall
constitute one and the same Agreement. In the event that any signature is
delivered by facsimile transmission, such signature shall create a valid
binding obligation of the party executing (or on whose behalf such signature
is executed) the same with the same force and effect as if such facsimile
signature were the original thereof.

                  (j) Governing Law. All questions concerning the
                      -------------
construction, validity, enforcement and interpretation of this Agreement
shall be governed by and construed and enforced in accordance with the
internal laws of the State of New York, without regard to the principles of
conflicts of law thereof. Each party agrees that all Proceedings concerning
the interpretations, enforcement and defense of the transactions

                                    -13-

contemplated by this Agreement (whether brought against a party hereto or
its respective Affiliates, employees or agents) shall be commenced
exclusively in the state and federal courts sitting in the City of New York,
Borough of Manhattan (the "NEW YORK COURTS"). Each party hereto hereby
irrevocably submits to the exclusive jurisdiction of the New York Courts for
the adjudication of any dispute hereunder or in connection herewith or with
any transaction contemplated hereby or discussed herein, and hereby
irrevocably waives, and agrees not to assert in any Proceeding, any claim
that it is not personally subject to the jurisdiction of any New York Court,
or that such Proceeding has been commenced in an improper or inconvenient
forum. Each party hereto hereby irrevocably waives personal service of
process and consents to process being served in any such Proceeding by
mailing a copy thereof via registered or certified mail or overnight
delivery (with evidence of delivery) to such party at the address in effect
for notices to it under this Agreement and agrees that such service shall
constitute good and sufficient service of process and notice thereof.
Nothing contained herein shall be deemed to limit in any way any right to
serve process in any manner permitted by law. Each party hereto hereby
irrevocably waives, to the fullest extent permitted by applicable law, any
and all right to trial by jury in any Proceeding arising out of or relating
to this Agreement or the transactions contemplated hereby. If either party
shall commence a Proceeding to enforce any provisions of this Agreement,
then the prevailing party in such Proceeding shall be reimbursed by the
other party for its attorney's fees and other costs and expenses incurred
with the investigation, preparation and prosecution of such Proceeding.

                  (k) Cumulative Remedies. The remedies provided herein are
                      -------------------
cumulative and not exclusive of any remedies provided by law.

                  (l) Severability. If any term, provision, covenant or
                      ------------
restriction of this Agreement is held by a court of competent jurisdiction
to be invalid, illegal, void or unenforceable, the remainder of the terms,
provisions, covenants and restrictions set forth herein shall remain in full
force and effect and shall in no way be affected, impaired or invalidated,
and the parties hereto shall use their reasonable efforts to find and employ
an alternative means to achieve the same or substantially the same result as
that contemplated by such term, provision, covenant or restriction. It is
hereby stipulated and declared to be the intention of the parties that they
would have executed the remaining terms, provisions, covenants and
restrictions without including any of such that may be hereafter declared
invalid, illegal, void or unenforceable.

                  (m) Headings. The headings in this Agreement are for
                      --------
convenience of reference only and shall not limit or otherwise affect the
meaning hereof.

                  (n) Independent Nature of Investors' Obligations and
                      ------------------------------------------------
Rights. The obligations of each Investor hereunder is several and not joint
------
with the obligations of any other Investor hereunder, and no Investor shall
be responsible in any way for the performance of the obligations of any
other Investor hereunder. The decision of each Investor to purchase
Securities pursuant to the Transaction Documents has been made independently
of any other Investor. Nothing contained herein or in any other agreement or
document delivered at any closing, and no action taken by any Investor
pursuant hereto or thereto, shall be deemed to constitute the Investors as a
partnership, an


                                    -14-

association, a joint venture or any other kind of entity, or create a
presumption that the Investors are in any way acting in concert with respect
to such obligations or the transactions contemplated by this Agreement. Each
Investor acknowledges that no other Investor has acted as agent for such
Investor in connection with making its investment hereunder. Except as
specified in the Transaction Documents, each Investor shall be entitled to
protect and enforce its rights, including without limitation the rights
arising out of this Agreement, and it shall not be necessary for any other
Investor to be joined as an additional party in any Proceeding for such
purpose.

                 [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK
                         SIGNATURE PAGES TO FOLLOW]


                                    -15-


                  IN WITNESS WHEREOF, the parties have executed this
Registration Rights Agreement as of the date first written above.

                           ZOLTEK COMPANIES, INC.

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

                 [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK
                   SIGNATURE PAGES OF INVESTORS TO FOLLOW]


                                    -16-


                  IN WITNESS WHEREOF, the parties have executed this
Registration Rights Agreement as of the date first written above.

                                   NAME OF INVESTING ENTITY

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

                                   AUTHORIZED SIGNATORY

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

                                   ADDRESS FOR NOTICE

                                   c/o:
                                        ---------------------------------

                                   Street:
                                           ------------------------------

                                   City/State/Zip:
                                                   ----------------------

                                   Attention:
                                              ---------------------------

                                   Tel:
                                            -----------------------------

                                   Fax:
                                            -----------------------------

                                   Email:
                                            -----------------------------


                                    -17-

                                                                       Annex A

                            Plan of Distribution

         The Selling Shareholders and any of their pledgees, donees,
transferees, assignees and successors-in-interest may, from time to time,
sell any or all of their shares of Common Stock on any stock exchange,
market or trading facility on which the shares are traded or in private
transactions. These sales may be at fixed or negotiated prices. The Selling
Shareholders may use any one or more of the following methods when selling
shares:

o    ordinary brokerage transactions and transactions in which the broker-
     dealer solicits investors;

o    block trades in which the broker-dealer will attempt to sell the shares
     as agent but may position and resell a portion of the block as
     principal to facilitate the transaction;

o    purchases by a broker-dealer as principal and resale by the broker-dealer
     for its account;

o    an exchange distribution in accordance with the rules of the applicable
     exchange;

o    privately negotiated transactions;

o    to cover short sales made after the date that this Registration Statement
     is declared effective by the Commission;

o    broker-dealers may agree with the Selling Shareholders to sell a specified
     number of such shares at a stipulated price per share;

o    a combination of any such methods of sale; and

o    any other method permitted pursuant to applicable law.

         The Selling Shareholders may also sell shares under Rule 144 under
the Securities Act, if available, rather than under this prospectus.

         Broker-dealers engaged by the Selling Shareholders may arrange for
other brokers-dealers to participate in sales. Broker-dealers may receive
commissions or discounts from the Selling Shareholders (or, if any
broker-dealer acts as agent for the purchaser of shares, from the purchaser)
in amounts to be negotiated. The Selling Shareholders do not expect these
commissions and discounts to exceed what is customary in the types of
transactions involved.

         The Selling Shareholders may from time to time pledge or grant a
security interest in some or all of the Shares owned by them and, if they
default in the performance of their secured obligations, the pledgees or
secured parties may offer and sell shares of Common Stock from time to time
under this prospectus, or under an amendment to this


                                    -18-

prospectus under Rule 424(b)(3) or other applicable provision of the
Securities Act of 1933 amending the list of selling shareholders to include
the pledgee, transferee or other successors in interest as selling
shareholders under this prospectus.

         Upon the Company being notified in writing by a Selling Shareholder
that any material arrangement has been entered into with a broker-dealer for
the sale of Common Stock through a block trade, special offering, exchange
distribution or secondary distribution or a purchase by a broker or dealer,
a supplement to this prospectus will be filed, if required, pursuant to Rule
424(b) under the Securities Act, disclosing (i) the name of each such
Selling Shareholder and of the participating broker-dealer(s), (ii) the
number of shares involved, (iii) the price at which such the shares of
Common Stock were sold, (iv)the commissions paid or discounts or concessions
allowed to such broker-dealer(s), where applicable, (v) that such
broker-dealer(s) did not conduct any investigation to verify the information
set out or incorporated by reference in this prospectus, and (vi) other
facts material to the transaction. In addition, upon the Company being
notified in writing by a Selling Shareholder that a donee or pledge intends
to sell more than 500 shares of Common Stock, a supplement to this
prospectus will be filed if then required in accordance with applicable
securities law.

         The Selling Shareholders also may transfer the shares of Common
Stock in other circumstances, in which case the transferees, pledgees or
other successors in interest will be the selling beneficial owners for
purposes of this prospectus.

         The Selling Shareholders and any broker-dealers or agents that are
involved in selling the shares may be deemed to be "underwriters" within the
meaning of the Securities Act in connection with such sales. In such event,
any commissions received by such broker-dealers or agents and any profit on
the resale of the shares purchased by them may be deemed to be underwriting
commissions or discounts under the Securities Act. Discounts, concessions,
commissions and similar selling expenses, if any, that can be attributed to
the sale of Securities will be paid by the Selling Shareholder and/or the
purchasers. Each Selling Shareholder has represented and warranted to the
Company that it acquired the securities subject to this registration
statement in the ordinary course of such Selling Shareholder's business and,
at the time of its purchase of such securities such Selling Shareholder had
no agreement or understanding, directly or indirectly, with any person to
distribute any such securities.

         The Company has advised each Selling Shareholder that it may not
use shares registered on this Registration Statement to cover short sales of
Common Stock made prior to the date on which this Registration Statement
shall have been declared effective by the Commission. If a Selling
Shareholder uses this prospectus for any sale of the Common Stock, it will
be subject to the prospectus delivery requirements of the Securities Act.
The Selling Shareholders will be responsible to comply with the applicable
provisions of the Securities Act and Exchange Act, and the rules and
regulations thereunder promulgated, including, without limitation,
Regulation M, as applicable to such Selling Shareholders in connection with
resales of their respective shares under this Registration Statement.

                                    -19-

         The Company is required to pay all fees and expenses incident to
the registration of the shares, but the Company will not receive any
proceeds from the sale of the Common Stock. The Company has agreed to
indemnify the Selling Shareholders against certain losses, claims, damages
and liabilities, including liabilities under the Securities Act.


                                    -20-