Maletz, Judge:
This case presents the question as to the proper tariff classification of footwear imported from Hong Kong that was described on the invoice as “Basketball High Shoes”. The imported footwear was classified under item 700.60 of the Tariff Schedules of the United States as “[fjootwear (whether or not described elsewhere in this subpart) which is over 50 percent by weight of rubber or plastics * * *” and assessed with duty at the rate of 20 percent ad valorem.
Plaintiff claims that this classification is erroneous and contends that the footwear is properly dutiable at 15 percent ad valorem under item 700.70 as “[fjootwear * * * [wjith soles of material other than leather, [wjith uppers of vegetable fibers”.
The pertinent provisions of the tariff schedules read as follows:
Classified under:
Footwear (whether or not described elsewhere in this subpart) which is over 50 percent by weight of rubber or plastics or over 50 percent by weight of fibers and rubber or plastics with at least 10 percent by weight being rubber or plastics:
***** * *
Other footwear (except footwear having uppers of which over 50 percent of the exterior surface area is leather) :
'f’ H» •}» ^ $ iji
700.60 Other- 20% ad val.
Claimed under:
Footwear, with uppers of fibers:
With soles of material other than leather:
700.70 With uppers of vegetable fibers_ 15% ad val.
Schedule 4, Part 4, Subpart B:
Subpart B headnotes:
1. This subpart covers all rubber whether or not obtained, derived, or manufactured in whole or in part from any product described in part 1 of this schedule.
2. For the purposes of the tariff schedules, the term “rubber” means a substance, whether natural or synthetic, in bale, crumb, powder, latex, or other crude form, which can be vulcanized or otherwise, cross-linked, and which after cross-linking can be stretched at 68 °F. to at least three times its original length and [61]*61which, after having been stretched to twice its original length and the stress removed, returns within 5 minutes to less than 150 percent of its original length, and includes such substance whether or not containing fillers, extenders, pigments, or rubber-processing chemicals.
At a pretrial conference, the parties entered into the following stipulation:
1. The uppers are of vegetable fibers.
2. The footwear is in no part of leather.
3. The midsoles of the instant footwear contain, as components, among other things, “Natural Eubber ESS” and “Synthetic Eubber’’. That “Natural Eubber ESS” and “Synthetic Eubber” are substances, whether natural or synthetic, in bale, crumb, powder, latex, or other crude form, which can be vulcanized or otherwise cross-linked, and which after cross-linking, can be stretched at .68° F. to at least three times its original length and which, after having been stretched to twice its original length and the stress removed, returns within 5 minutes to less than 150% of its original length.
4. Both parties agree to be bound by a determination by the Customs Laboratory as to whether the vulcanized so-called iron powder midsole material can be stretched to three times its original length.1
5. Defendant’s Collective Exhibit ‘A’ [a Customs Laboratory Eeport which was received in evidence without objection] is correct in its determination of the relative weights of the respective materials insofar as they were therein determined.
The Customs Laboratory Eeport thus referred to states in relevant part:
The midsoles in their present condition (containing the iron powder) are not capable of being stretched to three times their original length. In our opinion the rubber hydrocarbon of the midsole would conform to the physical requirements of the term “rubber” as defined in Headnote 2, Subpart B, Part 4, Schedule 4 of TSUSA 1969.
The weight of each sneaker minus the lacing was found to be 272 grams (left sneaker) and 283.5 grams (right sneaker). The midsoles were found to weigh 156.5 grams (left sneaker) and 169.2 grams (right sneaker). Three tests on the midsole of the left sneaker showed an average of 89% by weight of iron and iron oxide. This is equivalent to 51.2% by weight of the left sneaker minus the lacing. Assuming 89% by weight of iron and iron oxide in the right midsole, the right sneaker minus the lacing contains 53.1% iron and iron oxide.
* * * * % * *
Three tests on the midsole of the right sneaker showed an average of 89.5% by weight of iron and iron oxide. This is equivalent to 53.4% by weight of the right sneaker minus the lacing.
[62]*62Against tbis background, the issue is whether the midsole material— which, according to the Customs Laboratory Eeport, constitutes over 50 percent by weight of the imported footwear — consists solely of “rubber” as defined in headnote 2, schedule 4, part 4, subpart B. If it does, the parties agree that the classification of the footwear under item 700.60 must be upheld. On the other hand, if, as contended by plaintiff, (1) the midsole material consists of approximately 10 percent by weight of “rubber” as defined in headnote 2 and approximately 90 percent by weight of iron powder, or (2) is a “rubber compound” but not “rubber”, the classification must fall and the protest be sustained. Thus, resolution of the present controversy turns upon the interpretation of the term “rubber” as defined in headnote 2, schedule 4, part 4, subpart B.
We turn now to the record which, in addition to the stipulated matters set out above, consists of the testimony of two witnesses called by defendant, and assorted exhibits. The first witness, Joseph H. Fischer, who was employed originally as a chemist and is now a footwear specialist with Uniroyal, Inc., a domestic manufacturer of rubber and canvas footwear and sponge rubber products, testified that he is primarily responsible for the process development of rubber compounds prior to their fabrication into rubber products; and that he has practiced in the field of rubber chemistry for 23 years.
Henry S. Anthony, the second witness, who is chief chemist of the Tyer Rubber Division of the Converse Rubber Co., a domestic company, stated that he holds a degree in chemistry, has taken courses in rubber chemistry and technology, and has been in rubber technical work since 1937. He heads the laboratory at Tyer where he is in charge of the technical work, including compounding, quality development and testing, chiefly of rubber products.
According to the testimony of these witnesses, there are many “crude” natural and synthetic rubbers which come in latex (natural) form, and in bales, crumbs or sheets. Rubber molecules are basically hydrocarbons capable of being vulcanized2 or cross-linked, and are known as rubber polymers or elastomers. Elastomers are vulcanized commercially by means of curing or vulcanizing agents which consist of chemicals such as sulphur, peroxide or metal oxides that bind the rubber molecules together, i.e., perform the cross-linking. No rubbers are made commercially with only the elastomer and curing agent [63]*63as ingredients. Accelerators or activators, known as curing aids, are also used to speed up the process, and an antioxidant is generally added to protect tbe product from aging. The vulcanized or cured rubber is known as a “rubber compound” or “elastomer compound”.
The term “filler” refers to two classes of material: the reinforcing types, such as carbon black, which “actually enhance the rubber compounds, they give you better tensiles, better abrasion, make a product wear better”; and extenders which “[djegrade the product: * * * make it cheaper.” (E. 25) These ingredients are mixed together prior to vulcanization or curing.
The specific properties and characteristics of a rubber compound depend upon the type and quantity of fillers and other ingredients which are added to the elastomer and curing agent. Thus, if it is desired to make the compound light, a filler such as cork is added; to make the compound stiff, various types of resins are added; to make the compound heavy, fillers such as lead oxide are used. In short, the vulcanized product might be light, hard, soft, spongy, pigmented, or abrasion-resistant, and will vary in elasticity according to the fillers and pigments it contains.3 The elasticity can also be changed to a lesser extent by the curing or vulcanization system used.
All crude elastomers, with the necessary curing agents and accelerators can, without the addition of fillers or extenders, pass the statutory stretch test of headnote 2. But the fillers, extenders, pigments and rubber processing chemicals used may affect the vulcanized compound’s ability to pass the test. However, regardless of the degree of elasticity, if a vulcanized product contains an elastomer or rubber polymer, it is referred to in the industry as “rubber”, “rubber compound”, “elastomer” or “elastomer compound”.
Both witnesses produced various samples of vulcanized materials which they characterized as “rubber” or “rubber compounds”, and, in the case of an industrial sponge (Exhibit B-4), as a “finished rubber compound product”, although not all could pass the statutory stretch test.4 They considered these products to be rubber “[bjecause [64]*64the material which binds the whole mass together is rubber.”5 (R. 102; see also R. 61)
The ingredients contained in the midsoles of the imported shoes which are listed on the invoice accompanying the entry papers were characterized by both witnesses as a “rubber compound”.6
In connection with the production of synthetic rubbers, Fischer testified that his company manufactures, in combination with a Texas oil firm, a synthetic styrene-butadiene rubber called “Synpol”. For all intents and purposes, Fischer testified, neither this rubber nor the natural rubber purchased by his company contains fillers, extenders, pigments or rubber-processing chemicals.
However, Anthony testified, in the following exchange on cross-examination, that a “large amount” of “crude” styrene-butadiene (SBR) rubbers produced by the oil companies does contain fillers (R. 147):
Q. When crude rubber, either natural or synthetic, moves in commerce, does it not sometimes contain such things as pigments or fillers?
A. Well * * * [t]he manufacturers of SBR, the styrene buta-dience [sic] rubber, you see in many cases they are the big oil companies, and they are the companies that also, in some cases, manufacture carbon black, because they have oil and natural gas available, and they obviously produce oil, so there is a large amount of 8.B.É. which is manufactured with carbon blade arad oil in conjunction with the 8.B.R. elastomer, and that is sold under the name of a master batch.
Q. By number?
A. Yes. By many numbers, yes.
Q. Now, that master batch, is that capable of being cross-linked and then — as is, with the addition of sulphur — being cross-linked and then fitting the stretchability and return test that we have covered previously?
A. Yes.
Q. What would you characterize that carbon black as? Is it a filler?
A. As a reenforcing filler. [Emphasis added.]
As we have seen, the issue in this case is whether the midsole material — which constitutes over 50 percent by weight of the imported shoes — is “rubber” as defined in headnote 2. With respect to this issue, each party draws differing legal conclusions from the following [65]*65facts which, are not in dispute: (1) The imported footwear is in no part of leather and has uppers of vegetable fiber; (2) the midsoles contain as components, among other things, approximately 10 percent by weight of natural and synthetic rubbers which would conform to the physical requirements of “rubber” as defined in headnote 2; (3) the midsoles also contain, as components, approximately 89 to 89^ percent by weight of iron and iron oxide (iron powder) which constitute over 50 percent by weight of each shoe; (4) the midsoles in their finished condition do not meet the stretch test of headnote 2; and (5) the iron powder component is neither rubber, plastic nor vegetable fiber.
; In this setting, plaintiff, describing the midsole material as a “large amount of iron powder held together by [a] small amount of rubber acting in a sense, as a cement” (br. 9), contends that the iron powder is a separate constituent of the shoes and not part of the “rubber” of the midsoles since the mixture or compound formed by combining approximately 10 percent natural and synthetic rubber with 90 percent iron powder is not “ ‘such substance’ as is capable of being stretched to 3 times its length, etc., after cross-linking or vulcanization.” According to plaintiff, to meet the headnote 2 definition of “rubber”, the substance under consideration must in crude form be capable of being cross-linked or vulcanized, and thereafter be capable of meeting the stretch and return tests specified in headnote 2, whether or not it contains fillers, extenders, pigments or rubber-processing chemicals. Therefore, says plaintiff, even if the midsole material were considered to be a rubber compound because of the 10 percent rubber or elastomer content, it would not be rubber per se because of its inability to meet the stretch and return tests.
Defendant, on the other hand, claims that headnote 2 is clear and unambiguous and that the tests for “rubber” set out therein apply only to the “crude” substance, natural or synthetic rubber, when imported in bale, crumb, powder, latex, or other crude form. As to the imported midsoles, defendant’s position is that to constitute “rubber” within the meaning of headnote 2, it is only necessary that the substance used in the manufacture thereof be a natural or synthetic rubber, such as would meet the prescribed stretch and return tests — whether or not compounded by incorporating therein fillers, extenders, pigments or rubber-processing chemicals. In other words, defendant’s position is that if the substance in crude form is itself capable with a curing agent of being cross-linked and of meeting the stretch and return tests, any compound containing such substance is “rubber” even if the compound itself does not meet the prescribed stretch and return tests. Thus, defendant contends that the midsoles in question are “rubber” within the [66]*66meaning of headnote 2 because they contain as components, among others, elastomers which in crude form were capable of being cross-linked, and thereafter meeting the necessary stretch and return tests.
A brief filed by amicus curiae agrees with defendant’s interpretation of headnote 2 but, in support of its position, relies heavily upon the legislative history of the rubber definition as set out in the Tariff Classification Study, Nov. 15, 1960, schedule 4 (hereafter “Study”). That Study, as amicus notes, contains the original proposed schedule 4 which was released by the Tariff Commission on February 7, 1958, together with a notice of public hearings to be held thereon. In this connection, the headnote to subpart B, part 4, of the proposed schedule, as originally drafted, read as follows {Study, p. 247) :
Subpart B headnote:
1. The term “rubber”, in this subpart, means a substance in bale, crumb, powder, latex, or other crude form, whether or not containing fillers, extenders, pigments, or rubber-processing chemicals, which can be vulcanized or similarly processed into materials which can be stretched at 68° F. to at least twice their original length and which, after having been so stretched and the stress removed, return with force to approximately their original length.
This proposed definition, amicus concedes, would have made the vulcanization, stretch and return requirements applicable to a substance in crude form, with or without additives (fillers, extenders, etc.); hence, according to amicus, only those rubber compounds which were themselves capable of meeting the stretch tests would have been “rubber” for tariff purposes.
The final version of this headnote (renumbered headnote 2), as enacted by Congress, reads (as quoted previously) :
2. For the purposes of the tariff schedules, the term “rubber” means a substance, whether natural or synthetic, in bale, crumb, powder, latex, or other crude form, which can be vulcanized or otherwise cross-linked, and which after cross-linking can be stretched at 68° F. to at least three times its original length and which, after having been stretched to twice it original length and the stress removed, returns within 5 minutes to less than 150 percent of its original length, and includes such substance whether or not containing fillers, extenders, pigments, or rubber-processing chemicals.
Thus, in the final version of the headnote, the Tariff Commission (besides revising the physical requirements) changed the sentence structure by placing the “whether or not containing fillers * * *” clause at the end of the definition as part of the phrase “and includes such substance * * *.”
This change in sentence structure, amicus argues, is indicative of an intent by the Tariff Commission to limit the specified stretch and return tests to elastomers (rubber in crude form) not containing [67]*67fillers, extenders, etc., and to include within the definition of “rubber” elastomers containing fillers, extenders, etc. Stated otherwise, amicus contends, if the elastomer meets the stretch test, it is “rubber” and does not cease being “rubber” when fillers, extenders, etc. are added. Thus, in the view taken by amicus, it is irrelevant under the revised headnote whether or not a rubber compound can meet the specified stretch and return tests if it contains an elastomer which can.
However, as we read headnote 2 — -particularly in the context of the relevant legislative history — we cannot agree with this or with defendant’s interpretation of headnote 2. To the contrary, as we construe headnote 2, it refers to a substance in crude form, (not a “crude” substance) which (a) can be cross-linked and, after cross-linking, (b) meet the specified stretch and return tests; and it specifically includes, as subject to these requirements, all substances in crude form whether or not containing fillers, extenders, pigments or rubber-processing chemicals. In brief, in our view, the term “rubber”, for purposes of the tariff schedules, includes all substances in crude form, whether or not containing fillers, extenders, pigments or rubber-processing chemicals, which are capable of being cross-linked and of meeting the requisite stretch and return tests. This construction, we think, comports not only with the plain meaning of the language but with the express intent of the Tariff Commission which had been charged with the responsibility of revising and consolidating the tariff classification schedules.
As indicated in the Explanatory Notes and correspondence published in the previously referred to Study, the Commission was concerned with formulating a definition of rubber that would include, in addition to natural rubbers, those synthetic materials which were recognized by the industry and the Bureau of Customs as synthetic rubber, and which were being classified as such by the Bureau under paragraph 1558, Tariff Act of 1930, as modified by the General Agreement on Tariffs and Trade (T.D. 51802).7 See Study, p. 100. In formulating such a definition, the Commission was advised that it was important to recognize the distinguishing characteristics of rubber — i.e., cross-linking, elongation and reversible recovery capabilities — which would include synthetic rubbers that do not possess the properties of extensibility and retraction to the same degree as natural rubber, but would exclude resins and other materials. See Study, pp. 421-22. See also generally Study, pp. 408-35.8
[68]*68Following hearings held in March 1958 on proposed schedule 4 {Study, pp. 302 et seq.), the Tariff Commission’s legal staff held informal meetings and also corresponded with representatives of Polymer Corp. Ltd. of Sarnia, Canada, a large manufacturer and exporter of synthetic rubber, in order to settle upon a definition of rubber that (1) would contain less stringent stretch and permanent set requirements than were originally proposed; and (2) would ensure that definition’s applicability to recognized synthetic rubbers having lower permanent recovery capabilities such as Polymer’s Polysar SS — 250,” but would at the same time effectively screen out plastics and other non-rubber materials. Study, pp. 408-35.9
The final version of the headnote definition (aside from the reference to cross-linking) adopted Polymer’s recommended return test of “less than 150 percent” of the substance’s original length after elongation. The Commission’s almost total preoccupation with this aspect of the “rubber” definition is emphasized in the Explanatory ■ Notes, as follows (Study, pp. 100-01) :
Subpart B covering rubber has had substantial modifications made m its provisions since being published for public hearings. These modifications are reflected in headnotes 1 and 2 of sub-part B * * *.
The modifications reflected in headnotes 1 and 2 are primarily the result of further review of the customs practice of admitting certain coal-tar synthetic rubbers which are copolymers of styrene and butadiene under the provision for “synthetic rubber” m paragraph 1558 of the Tariff Act of 1930, as modified. At the time schedule 4 was published for hearings, this practice was under review and it appeared that it might be changed. However, subsequent to the publication of schedule 4 for public hearings, the Bureau of Customs reaffirmed its practice (TD 54726 (26)). Although there would seem to be considerable doubt as to the conclusion that a coal-tar synthetic rubber is not embraced [69]*69within the provisions of either paragraph 27 or 28, in view of the long-established practice, as recently reaffirmed, a number of informal meetings were held with interested parties with a view to obtaining a better understanding of the implications of this present practice.
The results of these informal meetings are reflected in headnotes 1 and 2. Headnote 1, together with a complementary change in the provisions of part 1 eliminating therefrom any reference to synthetic rubber, make it clear that subpart B covers all synthetic rubber whether or not obtained, derived, or manufactured in whole or in part from any coal-tar product described in part 1.
Headnote 2 concerns itself with the physical properties of rubbers. This definition is necessitated by virtue of the emergence of synthetic rubber as a commercial concept. Inasmuch as synthetic rubber is a man-made product, any definition attempting to equate it with its natural counterpart necessarily involves classification nuances which can be resolved only by arbitrary distinctions. The difficulty of arriving at a definition is demonstrated by the fact that the domestic industry has not yet been able to agree on all the factors involved in a precise definition.
In a preliminary draft of part 4B distributed to interested parties subsequent to the hearings, the definition of rubber was the same as that now incorporated in headnote % except that the part of the definition treating with permanent set would have required that the product return within five minutes to less than 110 percent of its original length. A comment received from the principal foreign shipper (see Appendix) indicated that 110 percent was too restrictive and would not include the very products that had been the subject of the long-continued customs practice. In the light of the representations made, in particular the assurances that the proposed change to 150 percent would not affect the status of another copolymer of styrene and butadiene which was the subject of CAD 546, the permanent set was changed to 150 percent. [Emphasis added.]
It appears from the best available information that the final definition of rubber would not change existing customs practices and, also, would include only those products which are properly known as synthetic rubbers.
*******
From what has been said, it is patent that the Commission’s primary intent in revising the rubber definition was to modify the stretch and return tests. There is not even a suggestion that the Commission at any time considered limiting these tests to elastomers without fillers, extenders, pigments or rubber-processing chemicals. Accordingly, the mere rearrangement of the “whether or not containing fillers, * * *” clause in nowise changed the meaning or effect of the definition with respect to the applicability of the requirements specified therein.
Furthermore, while defendant argues that the tests are limited to the so-called “crude” natural and synthetic rubbers, i.e., rubber polymers or elastomers not containing fillers, etc., it overlooks the uncontra-dicted testimony of its own witness Anthony (which has been previously quoted) that a large amount of crude synthetic rubber, known [70]*70as SBE, that is manufactured by oil companies and sold in commerce as “master batches”, contains oil — which is an extender — and carbon black — which is a “reenforcing filler”.
Thus, although the record establishes that crude natural rubber does not normally contain fillers, extenders, pigments or rubber-processing chemicals, there is a very substantial quantity of “crude” synthetic rubber that contains one or more of these compounding ingredients.10
Headnote 2 was intended to apply, as the Explanatory Notes make clear {Study, p. 100) to “coal-tar synthetic rubbers which are copolym-ers of styrene and butadiene”; this patently includes the “crude” SBE of commerce containing fillers. Under this headnote, there is no double standard for “rubber”; what applies to one elastomer containing fillers, extenders, etc. applies to all elastomers, whether they be “crude” or “compounded”. It thus must be concluded that the rubber definition applies in toto to all substances which meet the standards prescribed therein — whether or not compounded with fillers, etc.11
In short, whether the material comprising the midsoles of the imported shoes is “rubber” for purposes of the tariff schedules depends not upon what it is called in the trade, e.g., “rubber”, “rubber com[71]*71pound” or “rubber product”, but upon whether it meets the objective standards of headnote 2.12
This brings us to the heart of the matter. Can this midsole material — the “substance” in crude form containing fillers — be cross-linked and, after cross-linking, be stretched at 68° F. to at least three times its original length and then, after having been stretched to twice its original length and the stress removed return within 5 minutes to less than 150 percent of its original length ?
The midsoíe material can, of course, be cross-linked inasmuch as it is vulcanized. However, there is not a scintilla of evidence in the record that the midsole mixture or compound in crude form was incapable, after cross-linking, of meeting the specified stretch and return requirements. For the laboratory stretch test, by which the parties agreed to abide, was performed upon the finished midsoles. Eeliance upon this test is totally insufficient inasmuch as the undisputed testimony established that the method of curing or vulcanizing can affect the elasticity of the compound. (R. 71) The record is silent regarding the process used here; indeed, we are left completely unaware as to what extent or how the particular curing process used here may have affected the compound’s elastic capability. In the absence of stipulation or evidence linking the tests performed upon the finished product to the performance capability of the compound material in crude form, the stretchability of the finished midsole is irrelevant. For the finished midsole is not a substance in crude form to which the stretch and return tests of headnote 2 are applicable.
The basis of the classification here, which carries with it a presumption of correctness, is the classifying officer’s finding that the midsole consists solely of “rubber” as defined in headnote 2. Plaintiff has failed to establish that the midsole is not “rubber” as that term is so defined.
In sum, plaintiff has failed to discharge its burden of proof; hence, its protest must be overruled and the classification affirmed. Judgment will be entered accordingly.