OPINION
Chemcast Corporation appeals the judgment of the United States District Court for the Eastern District of Michigan that Claim 6 of United States Patent No. 4,081,-879 (’879 patent), the only claim in suit, is invalid because of the inventor’s failure to disclose the best mode as required by 35 U.S.C. § 112. See 12 USPQ2d 2005 (1989). We affirm.
Background
The ’879 patent claims a sealing member in the form of a grommet or plug button that is designed to seal an opening in, for example, a sheet metal panel. Claim 6, the only claim in suit, depends from Claim 1.
1. A grommet for sealing an opening in a panel, said grommet comprising an annular base portion having a continuous
circumferential and axial extending sealing band surface,
an annular locking portion having a continuous
circumferential and axial extending ridge portion approximately the same diameter as said sealing band surface,
said sealing band surface constituting an
axial extending continuation of said ridge portion,
said locking portion and said base portion *925 being in contact with each other and integrally bonded together,
said base portion comprising an elastom-eric
material and said locking portion being more rigid than said base portion,
whereby when the grommet is installed in a
panel opening, the locking portion is inserted through the opening to a position on the opposite side of the panel from the base portion locking the grommet in place, and said sealing band surface forms a complete seal continuously around the entire inner periphery of the panel opening.
6. The grommet as defined in claim 1 wherein the material forming said base portion has a durometer hardness reading of less than 60 Shore A and the material forming said locking portion has a durometer hardness reading of more than 70 Shore A. 1
The grommet of Claim 6 is referred to as a dual durometer grommet because it may be composed either of two materials that differ in hardness or of a single material that varies in hardness. In either case, the different hardnesses can be, and for a sufficiently large hardness differential must be, measured with different durometers: Shore A for the softer base portion and Shore D for the harder locking portion. The harder locking portion of the grommet is the focus of this case.
Chemcast and its competitor Arco Industries Corporation are both engaged in the manufacture and sale of sealing members such as grommets, gaskets, and plug buttons. Both sell their products primarily to the automobile industry. Ex-Arco employee Phillip L. Rubright founded Chemcast in 1973 and subsequently conceived of and designed specifically for Oldsmobile, a Chemcast customer, the dual durome-ter ’879 grommet. He filed a patent application together with an assignment of invention to Chemcast in January of 1976; the ’879 patent issued in April of 1978.
Chemcast subsequently sued Arco for infringement of Claim 6 of the ’879 patent. Arco counterclaimed that the patent was invalid on several grounds, including Ru-bright’s failure to comply with 35 U.S.C. § 112. The district court agreed. It held that, because the ’879 patent did not either disclose the best mode contemplated by the inventor of carrying out the invention or particularly point out and distinctly claim the subject matter of the invention, Chem-cast could not recover on its claim of infringement. 5 USPQ2d at 1238.
Both parties appealed. We vacated the district court’s best mode decision because, in reaching it, the court relied on an incorrect legal standard; reversed the court’s holding that Claim 6 did not meet the claim particularity requirements of section 112; and affirmed the judgment on all other issues.
Chemcast Corp. v. Arco Indus. Corp.,
Failure to comply with the best mode requirement amounts to concealing the preferred mode contemplated by the applicant at the time of filing. See Hybritech Inc. v. Monoclonal Antibodies, Inc.,802 F.2d 1367 , 1384-85,231 USPQ 81 , 94 (Fed.Cir.1986), cert. denied, [480 *926 U.S. 947,107 S.Ct. 1606 ,94 L.Ed.2d 792 ] (1987). In order for a district court to conclude that the best mode requirement is not satisfied, the focus must be, and the district court must determine, that the inventor knew of, i.e., “contemplated,” and concealed a better mode than he disclosed. Id.,231 USPQ at 94 . The focus for a best mode analysis is not simply on whether the patent discloses the most suitable material for carrying out the claimed invention.
Slip op. at 4. Accordingly, we remanded the case to the district court for a redeter-mination of the best mode issue.
On remand, the court again invalidated the patent for failure to satisfy the best mode requirement. Chemcast Corp. v. Arco Indus. Corp., 12 USPQ2d 2005 (E.D.Mich.1989). It made 47 factual findings detailing both what, at the time of filing the patent application, Rubright considered to be the best mode of practicing his claimed invention and what the specification as filed disclosed to one of ordinary skill in the art. According to the court, the principal shortcomings of the disclosure were its failure to specify (1) the particular type, (2) the hardness, and (3) the supplier and trade name, of the material used to make the locking portion of the grommet. Id. at 2008. Therefore, it held that the application as filed failed adequately to disclose the best mode of practicing the invention contemplated by Rubright. Id. Chemcast appeals.
Discussion
A.
The first paragraph of 35 U.S.C. § 112 (1982) provides:
The specification [A] shall contain a written description of the invention, and of the manner and process of making and using it, in such full, clear, concise, and exact terms as to enable any person skilled in the art to which it pertains, or with which it is most nearly connected, to make and use the same, and [B] shall set forth the best mode contemplated by the inventor of carrying out his invention.
(emphasis added). We long ago drew and often have focused upon the critical distinction between requirement [A], “enablement,” and requirement [B], “best mode.”
The essence of portion [A] is that a specification shall disclose an invention in such a manner as will enable one skilled in the art to make and utilize it. Separate and distinct from portion [A] is portion [B], the essence of which requires an inventor to disclose the best mode contemplated by him, as of the time he executes the application, of carrying out his invention. Manifestly, the sole purpose of this latter requirement is to restrain inventors from applying for patents while at the same time concealing from the public preferred embodiments of their inventions which they have in fact conceived.
In re Gay,
50 CCPA 725,
The best mode inquiry focuses on the inventor’s state of mind as of the time he filed his application — a subjective, factual question. But this focus is not exclusive. Our statements that “there is no objective standard by which to judge the adequacy of a best mode disclosure,” and that “only evidence of concealment (accidental or intentional) is to be considered,”
In re Sherwood,
Of necessity, the disclosure required by section 112 is directed to those skilled in the art.
Randomex Inc. v. Scopus Corp.,
The other objective limitation on the extent of the disclosure required to comply with the best mode requirement is, of course, the scope of the claimed invention. “It is concealment of the best mode of practicing the
claimed invention
that section 112 ¶ 1 is designed to prohibit.”
Randomex,
In short, a proper best mode analysis has two components. The first is *928 whether, at the time the inventor filed his patent application, he knew of a mode of practicing his claimed invention that he considered to be better than any other. This part of the inquiry is wholly subjective, and resolves whether the inventor must disclose any facts in addition to those sufficient for enablement. If the inventor in fact contemplated such a preferred mode, the second part of the analysis compares what he knew with what he disclosed — is the disclosure adequáte to enable one skilled in the art to practice the best mode or, in other words, has the inventor “concealed” his preferred mode from the “public”? Assessing the adequacy of the disclosure, as opposed to its necessity, is largely an objective inquiry that depends upon the scope of the claimed invention and the level of skill in the art.
Notwithstanding the mixed nature of the best mode inquiry, and perhaps because of our routine focus on its subjective portion, we have consistently treated the question as a whole as factual. “Compliance with the best mode requirement, because it depends on the applicant’s state of mind, is a question of fact subject to the clearly erroneous standard of review.”
Spectra-Physics,
B.
Chemcast alleges that the trial court erred in its best mode analysis by failing to focus, as required, on the claimed invention and on whether the inventor, Rubright, concealed a better mode than he disclosed. Neither allegation has any merit.
Chemcast first argues that, because the ’879 patent does not claim any specific material for making the locking portion of the grommet, Rubright’s failure to disclose the particular material that he thought worked the best does not violate the best mode requirement. This argument confuses best mode and enablement. A patent applicant must disclose the
best
mode of carrying out his claimed invention, not merely
a
mode of making and using what is claimed. A specification can be enabling yet fail to disclose an applicant’s contemplated best mode.
See Spectra-Physics,
Moreover, Chemcast is mistaken in its claim interpretation. While the critical limitation of Claim 6 is a hardness differential of 10 points on the Shore A scale between the grommet base and locking portions, and not a particular material type,
some
material meeting both this limitation and that of Claim 1, that “said base portion compris[e] an elastomeric material and said locking portion be[] more rigid than said base portion,” is claimed. That the claim is broad is no reason to excuse noncompliance with the best mode requirement. Here, the information the applicant is accused of concealing is not merely necessary to practice the claimed invention, as in
Dana
fluoride surface treatment was “necessary to satisfactory performance” of the claimed valve stem seal,
Chemcast’s second argument is equally misplaced. The court devoted no fewer than 13 factual findings to what the inven *929 tor Rubright knew as of the filing date of the ’879 application. Those findings focus, as did the parties, on the type, hardness, and supplier of the material used to make the locking portion of the grommet. 2 The court found that Rubright selected the material for the locking portion, a rigid polyvinyl chloride (PVC) plastisol composition; knew that the preferred hardness of this material was 75 + / — 5 Shore D; and purchased all of the grommet material under the trade name R-4467 from Reynosol Corporation (Reynosol), which had spent 750 man-hours developing the compound specifically for Chemcast. 12 USPQ2d at 2006-08. Furthermore, the court found that at the time the ’879 application was filed, the only embodiment of the claimed invention known to Rubright was a grommet composed of R-4467, a rigid PVC plas-tisol composition with a locking portion hardness of 75 + / — 5 Shore D. Id. at 2006.
In light of what Rubright knew, the specification, as issued, was manifestly deficient. It disclosed the following:
The annular locking portion [] of the sealing member [] is preferably comprised of a rigid castable material, such as a castable resinous material, either a thermoplastic or thermosetting resin, or any mixtures thereof, for example, polyurethane or polyvinyl chloride. The [locking] portion [ ] also should be made of a material that is sufficiently hard and rigid so that it cannot be radially compressed, such as when it is inserted in the opening [ ] in the panel [ ]. Materials having a durometer hardness reading of 70 Shore A or harder are suitable in this regard.
Col. 4, 11.53-63. The material hardness (75 Shore D) and supplier/trade name (Reyno-sol compound R-4467) are not explicitly disclosed here or anywhere else in the specification.
Nor, in light of the level of skill in the art, are they implicitly disclosed. Given the specification, one skilled in the art simply could not divine Rubright’s preferred material hardness. The court found that “the specification of the open-ended range of materials of ‘70 Shore A or harder’ conceals the best mode 75 Shore D material in part because materials of Shore A and Shore D hardnesses are recognized as different types of materials with different classes of physical properties.” 12 USPQ2d at 2008. As for the specific supplier and trade name designation of the preferred material, the court found that disclosing a list of generic potential materials was “not an adequate disclosure of the best mode PVC Re[y]nosol Compound R-4467.” Id.
We agree. That “at least eight other PVC composition suppliers [] could have formulated satisfactory materials for the dual durometer grommet,” 5 USPQ2d at 1235, does not, as Chemcast urges, excuse Rubright’s concealment of his preferred material, and the only one of which he was aware. Again Chemcast confuses enablement and best mode. The question is not whether those skilled in the art could make or use the ’879 grommet without knowledge of Reynosol compound R-4467; it is whether they could practice Rubright’s contemplated best mode which, the court found, included specifically the Reynosol compound. Rubright knew that Reynosol had developed R-4467 specifically for Chemcast and had expended several months and many hundred man-hours in doing so. 12 USPQ2d at 2007. Because Chemcast used only R-4467, because certain characteristics of the grommet material were claimed elements of the ’879 invention," and because Rubright himself did not know the formula, composition, or method of manufacture of R-4467, section 112 obligated Rubright to disclose the specific supplier and trade name of his preferred material.
*930
Other facts Chemcast points to as obviating the need for Rubright’s disclosure of “Reynosol R-4467” are simply irrelevant. That Reynosol considered the formulation of R-4467 a trade secret and that it offered the compound only to Chemcast,
id.,
do not bear on the state of Rubright’s knowledge or the quality of his disclosure. First, it is undisputed that Rubright did not know either the precise formulation or method of manufacture of R-4467; he knew only that it was a rigid PVC plastisol composition denominated “R-4467” by Reynosol. Whatever the scope of Reynosol’s asserted trade secret, to the extent it includes information known by Rubright that he considered part of his preferred mode, section 112 requires that he divulge it.
See White Consol. Indus. v. Vega Servo-Control,
Nor does the fact that Rubright developed his preferred mode with the requirements of a particular customer in mind excuse its concealment; compliance with section 112 does not turn on why or for whom an inventor develops his invention. An inventor need not disclose manufacturing data or the requirements of a particular customer
if
that information is not part of the best mode of practicing the claimed invention,
see Christianson,
Given the specification and the level of skill or understanding in the art, skilled practitioners could neither have known what Rubright’s contemplated best mode was nor have carried it out. Indeed, on these facts, they would not even have known where to look. This is not a case, like
Randomex,
where the inventor indiscriminately disclosed his preferred mode along with other possible modes.
See
In this situation and on these facts, where the inventor has failed to disclose the only mode he ever contemplated of carrying out his invention, the best mode requirement is violated.
See, e.g., Dana Corp.,
Conclusion
Accordingly, the judgment of the district court is affirmed.
AFFIRMED
Notes
. A device known as a durometer measures the hardness and softness of the materials used in the grommet. The Shore Instrument & Manufacturing Company is a leading manufacturer of durometers used for measuring rubber-like materials. A durometer referred to as a Shore A durometer measures soft, vulcanized rubber and all elastomeric materials, while a Shore D durometer measures rigid materials such as hard rubber and harder grades of plastic. The Shore B and Shore C durometers can be used to measure intermediate hardnesses.
There is some overlap in the range of use of the durometers. A conversion chart is published by the Shore Instruments & Manufacturing Co. which shows that the range of 30 to 100 on the scale of a Shore A durometer corresponds to the range of 6 to 58 on a Shore D durometer. The American Society for Testing Materials (ASTM) sets the standards to [sic, with] which the plastics and rubber industry comply [sic, complies] and recommends that hardnesses above 90 on the Shore A scale be measured with a Shore D durome-ter for greater accuracy.
Chemcast Corp. v. Arco Indus. Corp., 5 USPQ2d 1225, 1227 (E.D.Mich.1987).
. Prior to and at the time the '879 application was filed, Chemcast used a single type of material from a single supplier for both the base (soft) and locking (hard) portions of the grommet. Since the parties apparently do not dispute that the preferred hardness of the base portion was adequately disclosed, the district court focused, as will we, on the characteristics of the locking portion material.
