Case: 19-1243   Document: 70    Page: 1    Filed: 04/08/2020




   United States Court of Appeals
       for the Federal Circuit
                 ______________________

                BASF CORPORATION,
                  Plaintiff-Appellant

                           v.

      SNF HOLDING COMPANY, FLOPAM INC.,
      CHEMTALL, INC., SNF SAS, SNF (CHINA)
            FLOCCULANT CO. LTD.,
               Defendants-Appellees
              ______________________

                       2019-1243
                 ______________________

    Appeal from the United States District Court for the
 Southern District of Georgia in No. 4:17-cv-00251-RSB-
 BWC, Judge R. Stan Baker.
                 ______________________

                  Decided: April 8, 2020
                 ______________________

    JOHN C. O'QUINN, Kirkland & Ellis LLP, Washington,
 DC, argued for plaintiff-appellant. Also represented by
 GREGG LOCASCIO, SEAN M. MCELDOWNEY, CALVIN
 ALEXANDER SHANK; JAMES CHRISTOPHER MARTIN, Reed
 Smith LLP, Pittsburgh, PA; ROBERT RIDDLE, Houston, TX.

    JAMES W. DABNEY, Hughes Hubbard & Reed LLP, New
 York, NY, argued for defendants-appellees. Also repre-
 sented by EMMA L. BARATTA, STEFANIE MICHELLE
 GARIBYAN, PATRICE POLYXENE JEAN, RICHARD M. KOEHL,
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 2                BASF CORPORATION v. SNF HOLDING COMPANY




 DAVID E. LANSKY, MICHAEL M. POLKA; KHUE V. HOANG,
 Reichman Jorgensen LLP, New York, NY.
                ______________________
     Before LOURIE, MOORE, and CHEN, Circuit Judges.
 LOURIE, Circuit Judge.
      BASF Corporation appeals from a decision of the
 United States District Court for the Southern District of
 Georgia, granting summary judgment that claims 1 and 3–
 7 of U.S. Patent 5,633,329 (the “’329 patent”) are invalid as
 anticipated and that claim 2 is invalid as obvious. See
 BASF Corp. v. SNF Holding Co., No. 4:17-cv-00251-RSB-
 BWC (S.D. Ga. Oct. 4, 2018), ECF No. 355 (“Decision”). The
 district court concluded that a process performed by a third
 party, Celanese Corporation’s “Sanwet® Process,” evi-
 denced prior art knowledge and use of the patented inven-
 tion within the meaning of 35 U.S.C. § 102(a), and further
 constituted both a public-use bar and an on-sale bar to the
 patented invention under 35 U.S.C. § 102(b). 1
      For the reasons set forth below, we disagree and hold
 that the Sanwet® Process does not create an on-sale bar to
 the ’329 patent under § 102(b). We also conclude that the
 district court misinterpreted § 102(a) and the public-use
 bar of § 102(b), and that under the proper legal standard,
 genuine issues of material fact preclude the entry of sum-
 mary judgment on those issues. Accordingly, the judgment
 of the district court is reversed, and the case is remanded
 for further proceedings.



     1    The ’329 patent was filed in 1996 and issued in
 1997, so pre-AIA 35 U.S.C. § 102 applies. See Leahy–Smith
 America Invents Act (“AIA”), Pub. L. No. 112–29, § 3(c), 125
 Stat. 284, 293 (2011) (explaining that the pre-AIA version
 of the Patent Act generally applies to patents with effective
 filing dates before March 16, 2013).
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 4                 BASF CORPORATION v. SNF HOLDING COMPANY




 D1 (in red) represents the diameter of the reactor, D2 (in
 green) represents the diameter of the end of the conical ta-
 per, and α represents the angle between D1 and the wall of
 the conical taper. The conical taper starts at D1 and ends
 at D2. Claim 1 is representative 2:
     1. A process for preparing high molecular weight
     polymers, which comprises polymerizing water-sol-
     uble, monoethylenically unsaturated monomers
     and, if desired, crosslinkers which contain at least
     two nonconjugated, ethylenically unsaturated dou-
     ble bonds in the molecule, and, if desired, water-
     insoluble monoethylenically unsaturated mono-
     mers in aqueous solution in the presence of
     polymerization initiators
     in a tubular reactor which has a conical taper at
     the end, the ratio of the diameter of the reactor (D1)
     to the diameter at the end of the conical taper of
     the reactor (D2) being from 2:1 to 25:1 and the an-
     gle between D1 at the start of the conical taper and
     the inner cone wall being >45° and <90°, and
     removing the gelatinous reaction mixture by injec-
     tion of an inert gas.
     In 2014, BASF filed a complaint in the United States
 District Court for the Southern District of Texas alleging
 infringement of the ’329 patent by SNF Holding Company,
 Flopam Inc., Chemtall Inc., SNF SAS, and SNF (China)
 Flocculant Co. Ltd. (collectively, “SNF”). See BASF Corp.



     2   While BASF argues claim 2 separately on the issue
 of obviousness in view of the Sanwet® Process, we do not
 reach that issue in deciding this appeal. We also do not
 reach BASF’s argument that genuine issues of material
 fact preclude summary judgment of anticipation even in
 the event that the Sanwet® Process is prior art.
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 BASF CORPORATION v. SNF HOLDING COMPANY                    5



 v. SNF Holding Co., No. 4:14-cv-02733 (S.D. Tex. Sept. 23,
 2014). 3 SNF filed a petition in the U.S. Patent and Trade-
 mark Office for inter partes review of all claims of the ’329
 patent in January 2015, and the district court stayed this
 action. The Patent Trial and Appeal Board then held in a
 final written decision that SNF failed to prove any claim
 unpatentable on the ground of obviousness, SNF Holding
 Co. v. BASF Corp., No. IPR2015-00600, 2016 WL 8944638,
 at *10 (P.T.A.B. Aug. 2, 2016), and we affirmed, SNF Hold-
 ing Co. v. BASF Corp., 698 F. App’x 1034 (Fed. Cir. 2017).
     After the Board’s decision, SNF filed a motion for sum-
 mary judgment of invalidity, asserting that the Sanwet®
 Process anticipates claims 1 and 3–7 and renders claim 2
 obvious. The Sanwet® Process was created in Japan by
 Sanyo Chemical Industries Ltd. to manufacture super-
 absorbent polymers. Like the claimed invention, the San-
 wet® Process is a method for manufacturing high-
 molecular-weight polymers by polymerizing water-soluble,
 monoethylenically unsaturated monomers in aqueous solu-
 tion in the presence of polymerization initiators.
     In 1985, Sanyo and Celanese entered into a license
 agreement that provided Celanese with an exclusive li-
 cense to make, use, and sell certain of Sanyo’s superabsor-
 bent polymers in the Americas. In addition, Sanyo
 furnished Celanese with extensive technical information
 about the Sanwet® Process, dispatched technical personnel
 to assist Celanese with plant start-up, and guaranteed that
 Celanese’s Portsmouth, Virginia, plant would achieve the
 same performance as Sanyo’s own plant in Japan. Cela-
 nese was obligated to protect the secrecy of Sanyo’s



     3    In December 2017, the United States District
 Court for the Southern District of Texas granted SNF’s mo-
 tion to transfer venue to the United States District Court
 for the Southern District of Georgia.
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 6                 BASF CORPORATION v. SNF HOLDING COMPANY




 confidential information for ten years and was only allowed
 to disclose such information to its employees and subcon-
 tractors to the extent necessary to build and operate the
 plant. These employees and subcontractors were in turn
 required to sign confidentiality agreements. The license
 was paid up as of 1995, and the agreement terminated in
 1997.
      In its summary judgment order, the district court
 agreed with SNF that “one person’s use or knowledge” is
 all that is required for an invention to be “known or used”
 by others under § 102(a), and “whether prior use is secret
 or confidential is immaterial.” Decision, slip op. at 22–23.
 Under that standard, it found no genuine dispute that the
 Sanwet® Process was known and used in the United States
 by Celanese, Hoechst AG—which acquired Celanese in
 1987—and agents of Celanese, Hoechst, and Sanyo, as evi-
 denced by the technical information Sanyo provided Cela-
 nese and the extensive operation of the Portsmouth plant
 before the ’329 patent’s priority date of January 31, 1995.
 Id. at 24–25.
     The district court also granted summary judgment of
 invalidity on both the public-use and on-sale bars of
 § 102(b). 4 It found no genuine dispute that Celanese com-
 mercially exploited the Sanwet® Process before the critical
 date, and that its use was “in many respects accessible to
 the public.” Decision, slip op. at 28–29 (noting that Cela-
 nese and Hoechst gave tours of the Portsmouth plant and
 that a newspaper article depicted the plant’s interior). For
 the on-sale bar, the district court concluded that the license
 agreement, together with Sanyo’s technical information
 and in-person operations assistance, amounted to a sale,
 rather than just a license, because “the transmission of the


     4    The district court dismissed as moot BASF’s cross-
 motion for partial summary judgment of validity. Decision,
 slip op. at 35.
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 BASF CORPORATION v. SNF HOLDING COMPANY                        7



 process description to a user with the ability to perform the
 process constitutes putting the process ‘on-sale.’” Id. at 30–
 31 (citing Minton v. Nat’l Ass’n of Sec. Dealers, Inc., 336
 F.3d 1373, 1378 (Fed. Cir. 2003)).
     This appeal followed. We have jurisdiction pursuant to
 28 U.S.C. § 1295(a)(1).
                          DISCUSSION
      We review a district court’s grant of summary judg-
 ment according to the law of the regional circuit. Kaneka
 Corp. v. Xiamen Kingdomway Grp., 790 F.3d 1298, 1303
 (Fed. Cir. 2015) (citing Halo Elecs., Inc. v. Pulse Elecs., Inc.,
 769 F.3d 1371, 1377 (Fed. Cir. 2014)). In the Eleventh Cir-
 cuit, summary judgment is reviewed de novo, considering
 all evidence in the light most favorable to the nonmoving
 party. Sears v. Roberts, 922 F.3d 1199, 1205 (11th Cir.
 2019) (citing Hamilton v. Southland Christian School, Inc.,
 680 F.3d 1316, 1318 (11th Cir. 2012)). Summary judgment
 must be granted “if the movant shows that there is no gen-
 uine dispute as to any material fact and the movant is en-
 titled to judgment as a matter of law.” Fed. R. Civ. P. 56(a).
 But “at the summary judgment stage the judge’s function
 is not himself to weigh the evidence and determine the
 truth of the matter but to determine whether there is a
 genuine issue for trial.” Anderson v. Liberty Lobby, Inc.,
 477 U.S. 242, 249 (1986).
      Patent invalidity is an affirmative defense to an action
 for infringement. 35 U.S.C. § 282(b). The statutory pre-
 sumption of patent validity imposes the burden of persua-
 sion on the defendant, id. § 282(a), and factual propositions
 and inferences underlying an invalidity defense must be
 proven by clear and convincing evidence. Microsoft Corp.
 v. i4i Ltd. P’ship, 564 U.S. 91, 95 (2011).
     Pre-AIA 35 U.S.C. § 102 sets forth several conditions of
 patentability, including novelty (subsections (a), (e), (f),
 and (g)) and loss-of-right provisions which may,
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 8                 BASF CORPORATION v. SNF HOLDING COMPANY




 notwithstanding the novelty of an invention, bar a patent,
 id. (subsections (b), (c), and (d)). It provides that “[a] per-
 son shall be entitled to a patent unless,” inter alia, “(a) the
 invention was known or used by others in this country” be-
 fore the applicant’s invention, or “(b) the invention was . . .
 in public use or on sale in this country” more than one year
 before the applicant’s filing date. Anticipation is a question
 of fact, Duncan Parking Techs., Inc. v. IPS Grp., Inc., 914
 F.3d 1347, 1357 (Fed. Cir. 2019) (citing In re Gleave, 560
 F.3d 1331, 1334–35 (Fed. Cir. 2009)), but our interpreta-
 tion of the Patent Act is a question of law, see, e.g., Power
 Integrations, Inc. v. Semiconductor Components Indus.,
 LLC, 926 F.3d 1306, 1313–14 (Fed. Cir. 2019) (citing Un-
 wired Planet, LLC v. Google Inc., 841 F.3d 1376, 1379 (Fed.
 Cir. 2016)).
             I. § 102(a) Prior Knowledge or Use
     BASF first argues that the district court misinter-
 preted the phrase “known or used” in § 102(a) and errone-
 ously disregarded the confidentiality of Celanese’s
 knowledge and use. In BASF’s view, knowledge or use that
 is not publicly accessible does not qualify as prior art under
 § 102(a), and knowledge or use protected by confidentiality
 obligations is not publicly accessible. Because confidenti-
 ality agreements applied to both the technical information
 Sanyo provided Celanese concerning the Sanwet® Process
 and Celanese’s performance of that process in the Ports-
 mouth plant, BASF contends that neither is available as
 evidence of prior art knowledge or use.
     SNF responds that it has long been held that a single
 person’s knowledge or use is sufficient to defeat novelty.
 See Appellee Br. at 8–9 (citing Gayler v. Wilder, 51 U.S. (10
 How.) 477, 498 (1850); Coffin v. Ogden, 85 U.S. (18 Wall.)
 120, 124–25 (1873); UCB, Inc. v. Watson Labs. Inc., 927
 F.3d 1272, 1289–91 (Fed. Cir. 2019)). As a result, SNF ar-
 gues, the existence of a confidentiality restriction, or any
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 BASF CORPORATION v. SNF HOLDING COMPANY                      9



 other injunction of secrecy, upon those having knowledge
 of the invention is “simply extraneous.” Appellee Br. 30.
     We agree with BASF that the district court’s interpre-
 tation of § 102(a) was erroneous. This court has uniformly
 interpreted the “known or used” prong of § 102(a) to mean
 “knowledge or use which is accessible to the public.”
 Carella v. Starlight Archery & Pro Line Co., 804 F.2d 135,
 139 (Fed. Cir. 1986); accord Woodland Tr. v. Flowertree
 Nursery, Inc., 148 F.3d 1368, 1370 (Fed. Cir. 1998) (quoting
 Carella, 804 F.2d at 139), and Minn. Mining & Mfg. Co. v.
 Chemque, Inc., 303 F.3d 1294, 1306 (Fed. Cir. 2002).
     Our understanding traces back to our predecessor
 court, see In re Borst, 345 F.2d 851, 854 (CCPA 1965),
 which, in turn, derived its precedent from decisions of the
 Supreme Court, including Coffin and Gayler, and took
 guidance from renowned holdings of one of our sister cir-
 cuits, see, e.g., Metallizing Eng’g Co. v. Kenyon Bearing &
 Auto Parts Co., 153 F.2d 516 (2d Cir. 1946) (Hand, J.); Gill-
 man v. Stern, 114 F.2d 28 (2d Cir. 1940) (Hand, J.).
      The Patent Acts of 1790, ch. 7, § 1, 1 Stat. 109, 110, and
 1793, ch. 11, § 1, 1 Stat. 318, 319, created the original nov-
 elty requirement: that an invention could not be patented
 if it had been previously “known or used.” In Pennock v.
 Dialogue, 27 U.S. (2 Pet.) 1 (1829), the Supreme Court con-
 fronted the practical difficulties of treating the conduct of
 inventors and third parties equivalently for the purposes of
 novelty. A strict construction of “known or used” would ap-
 ply to the inventor’s own pre-filing knowledge and use, as
 well as that of the people he engaged to assist him. Thus, a
 patent’s novelty would often be defeated by its own reduc-
 tion to practice. To avoid such a result, the Court inter-
 preted “known or used” as implicitly limited to knowledge
 or use “by the public,” id. at 19, which was later codified in
 the Patent Act of 1836 as “by others,” before the date of
 invention. Ch. 357, § 6, 5 Stat. 117, 119.
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 10                BASF CORPORATION v. SNF HOLDING COMPANY




     The Supreme Court recognized, however, that its inter-
 pretation created a new problem.           If the inventor’s
 knowledge and use were so exempted, he could publicly use
 and sell his invention until “the danger of competition
 should force him to secure the exclusive right,” thereby ex-
 tending his effective exclusivity beyond the term provided
 by the statute. Pennock, 27 U.S. (2 Pet.) at 19. Pennock
 exemplifies that problem; there, the inventor publicly used
 and sold his invention for seven years before filing a patent
 application. Id. at 8. As a result, the Supreme Court in-
 terpreted the novelty requirement to also bar an inventor
 who publicly used or sold his invention from later obtaining
 a patent. Id. at 23–24 (“[The inventor’s] voluntary act or
 acquiescence in the public sale and use is an abandonment
 of his right . . . .”). Congress codified this distinction be-
 tween novelty and statutory bars in the Patent Act of 1836.
 Under that act, public use or sale of the invention before
 the inventor’s filing date barred a patent, but only if done
 “with [the inventor’s] consent or allowance.” Ch. 357, § 6,
 5 Stat. 117, 119. This provision was later modified to apply
 to public-use or on-sale activities of other parties as well.
 See Patent Act of 1870, ch. 230, § 24, 16 Stat. 198, 201; see
 also Andrews v. Hovey, 123 U.S. 267, 274 (1887).
     SNF contends that, by knowledge or use “accessible to
 the public,” Gayler, 51 U.S. (10 How.) at 497, the Supreme
 Court meant “existing” knowledge of any kind, secret or
 not, Appellee Br. 24, and provided an exception to the nor-
 mal rule that a patentee must be the first inventor only in
 the rare circumstance where the prior knowledge and use
 had been forgotten at the time of the patentee’s invention.
     We disagree. In Gayler, the Supreme Court affirmed a
 jury verdict for the patentee of no prior use or knowledge
 where the prior user “had not made his discovery public,
 but had used it simply for his own private purpose.” 51
 U.S. (10 How.) at 496. It held that the jury’s finding that
 the prior user’s device was “finally forgotten or abandoned”
 defeated the defendant’s prior knowledge and use defense
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 BASF CORPORATION v. SNF HOLDING COMPANY                      11



 because the patentee was similar to “the discoverer of a lost
 art,” and “whatever benefit any individual may derive from
 [the invention] . . . , he owes entirely to [the patentee].” Id.
 at 497–98.
      Gayler has long been held to rest on a broader principle
 than SNF advances: that one who invents something pre-
 viously known or used in a literal sense, but which has been
 forgotten, abandoned, concealed, or otherwise “lost,” is the
 first to “enrich[] the art” by his disclosure and is therefore
 the original inventor. Gillman, 114 F.2d at 31. Prior
 knowledge or use that is not accessible to the public “upon
 reasonable inquiry,” Gayler, 51 U.S. (10 How.) at 497, con-
 fers no benefit on the public, and thus does not suffice as a
 defense under § 102(a). In drafting the Patent Act of 1952,
 ch. 950, 66 Stat. 792, Congress “recogniz[ed] that the inter-
 pretation [of § 102(a)] by the courts excludes various kinds
 of private knowledge not known to the public.” H.R. Rep.
 No. 82-1923, at 6 (1952), reprinted in 1952 U.S.C.C.A.N.
 2394, 2399; see also P.J. Federico, Commentary on the New
 Patent Act (1954), 35 U.S.C.A. 1 (West 1954), reprinted
 in 75 J. PAT. TRADEMARK OFF. SOC’Y 161, 178 (1993) (noting
 that Congress did not intend to change these “narrowing
 interpretations”). Our precedent is in accordance with
 these authorities. See Woodland Tr., 148 F.3d at 1370.
     SNF is correct that “[p]rior knowledge and use by a sin-
 gle person is sufficient.” UCB, 927 F.3d at 1289 (quoting
 Coffin, 85 U.S. (18 Wall.) at 124). But “[t]he number is im-
 material,” Coffin, 85 U.S. (18 Wall.) at 125, and where the
 prior user has successfully concealed his work from the
 public, such prior knowledge or use is unavailable as prior
 art because the prior user has “not contributed to the store
 of knowledge” in the art, Woodland Tr., 148 F.3d at 1370.
 As we have noted in the context of the § 102(b) public-use
 bar, both the existence of relevant confidentiality agree-
 ments and the degree to which they were honored are evi-
 dence of whether prior knowledge and use were accessible
 to the public but are not necessarily conclusive. See, e.g.,
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 12                BASF CORPORATION v. SNF HOLDING COMPANY




 Bernhardt, L.L.C. v. Collezione Europa USA, Inc., 386 F.3d
 1371, 1379 (Fed. Cir. 2004) (citing Moleculon Research
 Corp. v. CBS, Inc., 793 F.2d 1261, 1266 (Fed. Cir. 1986),
 overruled-in-part on other grounds by Egyptian Goddess,
 Inc. v. Swisa, Inc., 543 F.3d 665 (Fed. Cir. 2008) (en banc)).
     The parties dispute the extent to which Sanyo’s tech-
 nical information and the performance of the Sanwet® Pro-
 cess at the Portsmouth plant were actually subject to
 confidentiality restrictions. SNF also argues that no evi-
 dence suggests Sanyo’s employees, who were sent to the
 United States to assist in the Portsmouth plant’s launch,
 were subject to the confidentiality obligations imposed on
 Celanese, its employees, and its agents. We conclude that
 the record reveals genuine issues of material fact as to
 whether the Sanwet® Process was “known or used” within
 the meaning of § 102(a), as set forth above. 5 We therefore
 reverse the district court’s summary judgment of invalidity
 and remand for a determination of SNF’s § 102(a) defense
 at trial.
                   II. § 102(b) Public Use
     BASF also argues that the district court’s summary
 judgment on public use was in error. Specifically, BASF
 contends that the district court misinterpreted the public-
 use bar of § 102(b) to apply to a third party’s secret com-
 mercial use. BASF also maintains that the district court’s
 other basis for its decision—that Celanese’s use of the San-
 wet® Process was not, in any event, secret—was erroneous
 because the record does not establish that members of the
 public could observe every step of the Sanwet® Process on
 tours Celanese gave of the Portsmouth plant or that it



      5   Our reversal of the district court’s summary judg-
 ment decision on public use, infra, cites additional genuine
 issues of material fact that may also bear upon the fact-
 finder’s evaluation of SNF’s § 102(a) defense.
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 BASF CORPORATION v. SNF HOLDING COMPANY                   13



 could get such information from the newspaper articles the
 district court cited.
     SNF responds that Celanese’s use of the Sanwet® Pro-
 cess was public under the holding of Electric Storage Bat-
 tery Co. v. Shimadzu, 307 U.S. 5, 20 (1939) (“The ordinary
 use of a machine or . . . process in a factory in the usual
 course of producing articles for commercial purposes is a
 public use.”). SNF further contends that a third party’s se-
 cret commercial use is a public-use bar regardless of its ac-
 cessibility to the public.
      We agree with BASF. In Shimadzu, the Supreme
 Court explained that the public-use bar applies to uses of
 the invention “not purposely hidden” and held that the use
 of a process in the ordinary course of business—where the
 process was “well known to the employees” and no “efforts
 were made to conceal” it from anyone else—is a public use.
 Id. at 20–21. In our public-use cases, we have applied the
 rule of Shimadzu to assess whether a use was successfully
 concealed or hidden and therefore inaccessible to the pub-
 lic. See, e.g., Motionless Keyboard Co. v. Microsoft Corp.,
 486 F.3d 1376, 1384–85 (Fed. Cir. 2007); Invitrogen Corp.
 v. Biocrest Mfg., L.P., 424 F.3d 1374, 1382 (Fed. Cir. 2005);
 New Railhead Mfg., L.L.C. v. Vermeer Mfg. Co., 298 F.3d
 1290, 1297 (Fed. Cir. 2002); W.L. Gore & Assocs., Inc. v.
 Garlock, Inc., 721 F.2d 1540, 1548–50 (Fed. Cir. 1983). If
 the use identified by the defendant was not successfully
 concealed or hidden from those who lack any “limitation or
 restriction, or injunction of secrecy,” Egbert v. Lippmann,
 104 U.S. (14 Otto) 333, 336 (1881), then it is a public use
 within the meaning of § 102(b). But see, e.g., City of Eliza-
 beth v. Am. Nicholson Pavement Co., 97 U.S. 126, 133–37
 (1877) (experimental use is not public use).
     The parties disagree whether Celanese’s use of the
 Sanwet® Process meets this standard. The district court
 cited evidence that Celanese had given tours of the Ports-
 mouth plant to local officials, potential customers, and
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 14                BASF CORPORATION v. SNF HOLDING COMPANY




 members of the public and that newspaper articles and a
 commemoration video depicted the interior of the plant.
 Decision, slip op. at 28. BASF principally contends that,
 while certain elements of the claimed process were unques-
 tionably made public—such as the shape of the conical ta-
 per—the rest were not, precluding a finding of public use.
 SNF responds that Celanese failed to fully conceal the pro-
 cess, which qualifies as public use as a matter of law.
     We conclude that the district court erred in finding, on
 summary judgment, that the claimed process was publicly
 accessible. As an initial matter, we disagree with BASF
 that public use under § 102(b) requires a finding that the
 public was made aware of every limitation of the claimed
 process. Our precedent is clear that a factfinder should
 consider whether certain elements of the claimed invention
 were already in the public domain at the time of the alleged
 public-use or on-sale activity. Thus, we have held that
 § 102(b) “does not require a strict identity between the
 claimed invention and the device involved in the public use
 or on sale activities;” it only requires that “the differences
 between the claimed invention and the device used or sold
 would have been obvious to one skilled in the art.” In re
 Smith, 714 F.2d 1127, 1137 n.13 (Fed. Cir. 1983) (citing In
 re Corcoran, 640 F.2d 1331, 1333 (CCPA 1981)); see also In
 re Blaisdell, 242 F.2d 779, 783 (CCPA 1957) (finding public
 use even where some elements of the invention are by their
 nature concealed from view) (citing Hall v. Macneale, 107
 U.S. (17 Otto) 90, 96–97 (1883)).
     But, on this record, genuine issues of material fact pre-
 vent entry of summary judgment on SNF’s public-use de-
 fense. Neither party disputes that members of the public
 were given access to the Portsmouth plant on numerous oc-
 casions, where they could view the shape of the conical ta-
 per, and that no evidence suggests that any of these guests
 was a skilled artisan. The parties dispute whether the re-
 maining elements of the Sanwet® Process were known, and
 to the extent they were not, whether they were concealed
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 BASF CORPORATION v. SNF HOLDING COMPANY                    15



 from the public on these tours, in newspaper articles, and
 in the commemoration video. While the public-use inquiry
 is often context-specific, we have identified factors which
 may, in a given case, prove relevant. See, e.g., Dey, L.P. v.
 Sunovion Pharm., Inc, 715 F.3d 1351, 1355–56 (Fed. Cir.
 2012) (the nature of the activity that occurred in public,
 public access to and knowledge of the public use, existence
 of an actual or implied confidentiality obligation, and the
 relevant skill and knowledge of observers (citations omit-
 ted)). A factfinder would be entitled to make reasonable
 inferences about these activities in deciding whether Cela-
 nese’s use of the Sanwet® Process was a public use, and
 summary judgment is therefore improper. See id. at 1357
 (“The ‘public use’ inquiry is replete with factual considera-
 tions . . . .”); Barry v. Medtronic, Inc., 914 F.3d 1310, 1327
 (Fed. Cir. 2019) (acknowledging that the jury is permitted
 to make reasonable inferences about public accessibility
 and confidentiality).
      SNF’s second contention—that a third party’s commer-
 cial exploitation of a secret process creates a per se public-
 use bar to another inventor—is simply wrong. In Gore, this
 court held that a third party’s sale of products made by a
 secret process, more than one year before the critical date,
 does not create a bar to another inventor patenting the pro-
 cess. 721 F.2d at 1550 (citing Metallizing, 153 F.2d 516).
      In Metallizing, the defendant raised a public-use de-
 fense based on the patentee’s earlier commercial exploita-
 tion of his then-secret process. Judge Learned Hand,
 writing for the Second Circuit, recognized that a secret pro-
 cess was neither “publicly” used, nor itself on sale, under a
 literal construction of § 102(b). Nevertheless, he reasoned
 that an inventor’s commercial exploitation of the secret
 process squarely implicated the Supreme Court’s rationale
 for creating the statutory bars in the first place, see Pen-
 nock, 27 U.S. (2 Pet.) 1, and that the statute would be frus-
 trated were such an exception recognized. Metallizing, 153
 F.2d at 519–20. Thus, the Second Circuit held that an
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 16                BASF CORPORATION v. SNF HOLDING COMPANY




 inventor’s commercial exploitation of his invention before
 the critical date created a public-use bar—“regardless of
 how little the public may have learned about the inven-
 tion.” Id. at 520 (“[I]t is a condition upon an inventor’s
 right to a patent that he shall not exploit his discovery com-
 petitively after it is ready for patenting; he must content
 himself with either secrecy, or legal monopoly.”). At the
 same time, Metallizing reaffirmed the holding of Gillman,
 114 F.2d at 30–31, that such exploitation by a third party
 does not create a public-use bar. 153 F.2d at 518–19. The
 Metallizing rule was subsequently adopted as precedent by
 this court in Gore, 721 F.2d at 1550. 6 See also Pfaff v. Wells
 Elecs., Inc., 525 U.S. 55, 68–69 (1998) (citing the Metalliz-
 ing rule); Bonito Boats, Inc. v. Thunder Craft Boats, Inc.,
 489 U.S. 141, 149 (1989) (same).
      Nevertheless, SNF argues that Metallizing forfeiture is
 equally applicable to third-party secret uses, citing our de-
 cision in Invitrogen Corporation v. Biocrest Manufacturing,
 L.P., 424 F.3d 1374 (Fed. Cir. 2005). SNF is mistaken.
 Invitrogen concerned a patentee that had used its process
 for internal purposes before seeking a patent. We reversed
 the district court’s finding of public use because the process
 had been successfully concealed until after the critical date.
 Id. at 1379. We also noted that the Metallizing rule was
 inapplicable in that case because the record showed that
 Invitrogen never commercially exploited the process or




      6   Unsurprisingly, given its judicial provenance, the
 Metallizing rule has been variously applied by this court as
 a public-use bar and as an on-sale bar. Compare Kinzen-
 baw v. Deere & Co., 741 F.2d 383, 390 (Fed. Cir. 1984) (pub-
 lic-use), with Quest Integrity USA, LLC v. Cokebusters USA
 Inc., 924 F.3d 1220, 1227 (Fed. Cir. 2019) (on-sale). For the
 purposes of this appeal, we treat it as the district court
 did—as a public-use bar.
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 BASF CORPORATION v. SNF HOLDING COMPANY                     17



 attempted to do so. Id. at 1382–83. Invitrogen did not con-
 cern third-party public use at all. 7
      Moreover, as we reasoned in Gore, extending the Met-
 allizing rule to third-party public use, as SNF urges, is in-
 consistent with § 102(b). The primary reasons for the
 statutory bars are to prevent the public from being de-
 prived of that which it has come to rely on as publicly avail-
 able, to encourage prompt disclosure of inventions, and to
 prevent effective extension of patent term by gamesman-
 ship. See TP Labs., Inc. v. Prof. Positioners, Inc., 724 F.2d
 965, 968 (Fed. Cir. 1984). The Metallizing rule as it stands
 fulfills the latter two imperatives, and it is not inconsistent
 with the first because a secret process is not in the public
 domain in the first place. See, e.g., Gore, 721 F.2d at 1550
 (patent law favors the later inventor who shares his
 knowledge with the public over the prior inventor who con-
 ceals his invention). 8




     7    SNF also misreads J.A. LaPorte, Inc. v. Norfolk
 Dredging Co., 787 F.2d 1577 (Fed. Cir. 1986), to conflict
 with Gore. In that case, we held only that a third party’s
 secret sale of a device created an on-sale bar to a later in-
 ventor’s patent on the same device—an unremarkable
 proposition, see, e.g., Helsinn Healthcare S.A. v. Teva
 Pharm. USA, Inc., 139 S. Ct. 628 (2019).
      8   It also appears that Congress has considered the
 implications of patenting secret processes, which prior in-
 novators might often choose to conceal as trade secrets, and
 addressed the issue. As part of the AIA, § 5, 125 Stat. 284,
 297–99, Congress revised 35 U.S.C. § 273 to create a prior-
 use defense for a defendant that “commercially used” a
 claimed “process” or “machine, manufacture, or composi-
 tion of matter used in a manufacturing or other commercial
 process” “at least 1 year” before the earlier of the effective
 filing date of the claimed invention or a previous disclosure
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 18                BASF CORPORATION v. SNF HOLDING COMPANY




     In summary, we reverse the district court’s summary
 judgment of invalidity and remand for determination of
 SNF’s public-use defense at trial.
                     III. § 102(b) On Sale
     BASF further requests reversal of the district court’s
 decision on SNF’s § 102(b) on-sale defense. It argues that
 the agreement between Sanyo and Celanese to license the
 Sanwet® Process was not a sale under In re Kollar, 286 F.3d
 1326 (Fed. Cir. 2002). BASF further denies that Hoechst’s
 acquisition of Celanese in 1987, including the operational
 Portsmouth plant, constitutes a sale of the process.
      SNF responds that the facts of this case differ from
 those in Kollar. It emphasizes that the Sanwet® Process
 was fully operational at the time of the license and Sanyo
 was contractually obligated to help Celanese meet perfor-
 mance      guarantees      for    the    Portsmouth      plant.
 SNF submits that Minton, 336 F.3d 1373, cited by the dis-
 trict court, held that the on-sale bar applies to a conveyance
 of a product that enables the recipient to perform a later-
 claimed process, and it argues that Minton controls this
 case. Alternatively, SNF argues that we should affirm the
 district court’s judgment because Hoechst’s acquisition of
 Celanese separately placed the Sanwet® Process on sale.
     We agree with BASF that the district court’s judgment
 must be reversed. Neither the Sanyo-Celanese license
 agreement nor the 1987 Hoechst acquisition of Celanese is
 a sale of the invention within the meaning of § 102(b).
     An invention is “on sale” under § 102(b) when it is “the
 subject of a commercial offer for sale,” and is ready for pa-
 tenting. Pfaff, 525 U.S. at 67. The invention itself must be
 sold or offered for sale, and the mere existence of a



 thereof. A successful prior-use defense, however, does not
 necessarily establish invalidity. 35 U.S.C. § 273(g).
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 BASF CORPORATION v. SNF HOLDING COMPANY                      19



 “commercial benefit . . . is not enough to trigger the on-sale
 bar” on its own. Medicines Co. v. Hospira, Inc., 827 F.3d
 1363, 1373 (Fed. Cir. 2016) (en banc). To determine
 whether such a commercial sale or offer for sale has oc-
 curred, we look to how those terms are defined in the Uni-
 form Commercial Code. Id. at 1365, 1375 (“[T]he Uniform
 Commercial Code describes a ‘sale’ as ‘the passing of title
 from the seller to the buyer for a price.’ U.C.C. § 2-106(1).”);
 Group One, Ltd. v. Hallmark Cards, Inc., 254 F.3d 1041,
 1048 (Fed. Cir. 2001) (“[A] commercial offer for sale [under
 § 102(b) is] one which the other party could make into a
 binding contract by simple acceptance (assuming consider-
 ation) . . . .”).
     But we have often recognized that “[a] process, how-
 ever, is a different kind of invention; it consists of acts, ra-
 ther than a tangible item,” Kollar, 286 F.3d at 1332, as is
 contemplated by the U.C.C.’s definition of sale. Yet, in cer-
 tain circumstances, a process may be sold in a manner
 which triggers the on-sale bar. For example, performing
 the process itself for consideration is sufficient. See Scal-
 tech, Inc. v. Retec/Tetra, LLC, 269 F.3d 1321, 1328–29
 (Fed. Cir. 2001) (offer to perform process for treating oil re-
 finery waste placed the invention on sale). So is a pa-
 tentee’s sale of a product made by his later-patented
 process, i.e., the Metallizing rule. D.L. Auld Co. v. Chroma
 Graphics Corp., 714 F.2d 1144, 1147–48 (Fed. Cir. 1983)
 (applying the Metallizing rule as an on-sale bar).
      In Kollar, this court decided that a chemical process for
 preparing peroxides was not placed on sale by the pa-
 tentee’s contract with Celanese, which called for Kollar to
 license his future patents covering the invention, provide
 Celanese with technical “know-how” for implementing the
 process, and to coordinate possible future commercializa-
 tion, in exchange for a royalty. We first explained that no
 products made using Kollar’s process had ever been sold or
 offered for sale, and, as a result, potential plans to commer-
 cialize the invention in the future were irrelevant. 286
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 20                BASF CORPORATION v. SNF HOLDING COMPANY




 F.3d at 1330–31. Absent such a forfeiture, D.L. Auld, 714
 F.2d 1144, the arrangement amounted to an ordinary li-
 cense agreement. Thus, the holding of Kollar rested on the
 well-established principle that the grant of a license to
 practice a patented invention, with or without accompany-
 ing technical information, does not itself create an on-sale
 bar. Id. at 1333; see Mas-Hamilton Grp. v. LaGard, Inc.,
 156 F.3d 1206, 1216–17 (Fed. Cir. 1998); Moleculon, 793
 F.2d at 1267.
     Shortly thereafter, we decided Minton, which con-
 cerned a computer system programmed to facilitate securi-
 ties trading and methods of doing so using the claimed
 system. We held there that, unlike the transaction at issue
 in Kollar, Minton’s lease of his trading system to a local
 brokerage firm raised an on-sale bar against his method
 claims because the system substantially “embod[ied] the
 claimed method.” 336 F.3d at 1378; see also J.A. LaPorte,
 787 F.2d at 1583.
      As the Supreme Court observed, in the context of the
 patent exhaustion doctrine, a product and methods of using
 that product “may approach each other so nearly that it
 will be difficult to distinguish the process from the function
 of the apparatus.” Quanta Comput., Inc. v. LG Elecs., Inc.,
 553 U.S. 617, 629 (2008) (quoting United States ex rel.
 Steinmetz v. Allen, 192 U.S. 543, 559 (1904)). In that cir-
 cumstance, where a product “embodie[s] essential features
 of [the] patented invention,” Quanta, 553 U.S. at 632 (quot-
 ing United States v. Univis Lens Co., 316 U.S. 241, 249–51
 (1942)), a sale of the product is tantamount to a sale of the
 process performed by that product and thus creates an on-
 sale bar to the process claims as well. See Minton, 336 F.3d
 at 1377–78.
     Under these precedents, it is clear that Kollar governs
 this case. The Sanyo-Celanese agreement provided Cela-
 nese with a license to practice the Sanwet® Process, ex-
 haustive technical information about performing it, and
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 BASF CORPORATION v. SNF HOLDING COMPANY                  21



 the in-person assistance of Sanyo’s employees. This agree-
 ment differs from Kollar’s license agreement with Celanese
 only to the extent that Sanyo might have provided Cela-
 nese with more assistance to enable it to perform the
 claimed process, but it was not a sale of the Sanwet® Pro-
 cess.
     The district court’s error arose from its misunderstand-
 ing of our holding in Minton—as does SNF’s for that mat-
 ter. As we explained above, Minton did not hold that
 transmitting information about an operative process to en-
 able a licensee to perform it invokes the on-sale bar. The
 on-sale bar does not turn on whether or not the patentee’s
 process information and assistance are helpful to the licen-
 see or whether the licensee is capable of performing the li-
 censed process. Unlike in Minton, the essential features of
 the claimed process here were not embodied in a product
 sold or offered for sale before the critical date.
     Finally, we reject SNF’s argument for its alternative
 ground of affirmance. Hoechst’s acquisition of Celanese did
 not create an on-sale bar for the same reason that the
 Sanyo-Celanese license did not: there was no product sold
 as part of the transaction that embodied the essential fea-
 tures of the Sanwet® Process. While SNF argues that ei-
 ther the Portsmouth plant itself or the plant’s equipment
 used to perform the Sanwet® Process is such a product, we
 disagree. The record contains no indication that the equip-
 ment substantially embodies the claimed process; indeed,
 SNF’s declarant asserted that the reactors used were “con-
 ventional polymerizing vessel[s].” J.A. 4219. In other
 words, the equipment was capable of numerous uses apart
 from its use in the Sanwet® Process and therefore does not
 substantially embody the essential features of the ’329 pa-
 tent claims. See Quanta, 553 F.3d at 631–32. It follows,
 a fortiori, that neither does the entire Portsmouth plant or
 all of Celanese as it existed before its acquisition by
 Hoechst. For a typical acquisition such as this, the pur-
 chase of a company is not, under the patent law,
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 22                BASF CORPORATION v. SNF HOLDING COMPANY




 tantamount to a purchase, or in inverse terms a sale, of
 every asset held by the acquired company. See Micro-Mag-
 netic Indus., Inc. v. Advance Automatic Sales Co., 488 F.2d
 771, 772–73 (9th Cir. 1973).
      We reverse the district court’s decision and hold that
 the ’329 patent claims are not invalid under the on-sale bar
 of § 102(b).
                        CONCLUSION
     We have considered the parties’ remaining arguments
 but find them unpersuasive. Because the district court
 misinterpreted § 102(a) prior knowledge and use, as well
 as the public-use bar of § 102(b), we reverse its summary
 judgment and remand for trial on those defenses. We also
 reverse the district court’s summary judgment on SNF’s
 on-sale bar defense and direct entry of partial summary
 judgment for BASF on that issue. Accordingly, the judg-
 ment of the district court is
                REVERSED AND REMANDED
                           COSTS
      Costs to BASF.
