Public use bar
An invention placed in public use before the critical date — one year before filing under § 102(b)(1)'s grace period — is barred from patenting. The doctrine reaches uses that are not strictly "public" in any colloquial sense; Egbert v. Lippmann famously held that an inventor's wife wearing a corset spring with no obligation of secrecy was a public use that defeated her husband's patent.
The rule
A claim is invalid under 35 U.S.C. § 102(a)(1) if the invention was "in public use" before the effective filing date of the application. Section 102(b)(1) provides a one-year grace period for the inventor's own pre-filing disclosures. The "critical date" for the public-use analysis is therefore one year before the effective filing date.
Under Egbert v. Lippmann, 104 U.S. 333 (1881), an invention is in public use when it has been used by a person other than the inventor, where that person is under no limitation, restriction, or obligation of secrecy to the inventor. Id. at 336. The use need not be visible to the public at large. The wife's two corset springs, hidden from view under her clothes for eleven years, were a public use because she wore them without any obligation of confidentiality. Id. at 337–38.
The modern test is sometimes phrased as "public accessibility" — was the invention accessible to the public, or to one or more members of the public who were under no obligation of secrecy. American Seating Co. v. USSC Group, Inc., 514 F.3d 1262 (Fed. Cir. 2008). The Pfaff "ready for patenting" prong applies: a use cannot be public until the invention is ready for patenting.
Statutory and constitutional source
The public-use bar is statutory. Pre-AIA § 102(b) (2006) barred patents where the invention was "in public use or on sale in this country, more than one year prior" to filing. The AIA replaced this with § 102(a)(1), which bars patents where the invention was "in public use, on sale, or otherwise available to the public before the effective filing date."
Two changes are textually significant. First, the AIA dropped the geographic limitation "in this country." Public uses anywhere in the world now count. This conforms § 102(a)(1) to international practice. Second, the AIA added the catchall "or otherwise available to the public," raising the question whether "in public use" must now mean publicly accessible (as opposed to Egbert-style hidden use). Congress and the courts have not definitively answered this question; the Federal Circuit has indicated the historical understanding survives where the use is non-secret. See Helsinn Healthcare S.A. v. Teva Pharmaceuticals USA, Inc., 586 U.S. 123 (2019) (holding that the AIA's "on sale" carries forward the pre-AIA understanding).
The constitutional foundation is the Patent and Copyright Clause's "limited Times" requirement, U.S. Const. art. I, § 8, cl. 8. The public-use and on-sale bars together prevent inventors from extending the patent monopoly by exploiting an invention publicly before filing. Pennock v. Dialogue, 27 U.S. (2 Pet.) 1, 19 (1829) (Story, J.).
The framework the courts apply
Use of the claimed invention
The asserted public use must be of the claimed invention, with every limitation in operation. A demonstration of a non-claimed feature, even of a related product, does not trigger the bar. Lockwood v. American Airlines, Inc., 107 F.3d 1565 (Fed. Cir. 1997).
Public accessibility / no duty of secrecy
The use must be by someone other than the inventor without a confidentiality obligation. The inventor's own use does not trigger the bar (subject to the experimental-use analysis below); a competitor's independent use also does not trigger the inventor's grace period under § 102(b)(2)(A) but may itself create § 102(a) prior art. The leading factual question is whether the user owed a duty of confidentiality at the time of the use.
Egbert is the paradigm: the wife's wearing of the corset spring was unrestricted, the inventor took no steps to require secrecy, and a third party who later examined and discussed the invention did so without restriction. The use was therefore public even though no member of the general public ever saw the spring. 104 U.S. at 337–38.
By contrast, in Moleculon Research Corp. v. CBS, Inc., 793 F.2d 1261 (Fed. Cir. 1986), the inventor showed a Rubik's-Cube-style puzzle to colleagues and friends in informal settings; the Federal Circuit held this was not a public use because the inventor retained control of the puzzle and reasonably expected confidentiality from a small, identified group. The contrast with Egbert turns on retained control and reasonable expectations.
Ready for patenting
Pfaff v. Wells Electronics, Inc., 525 U.S. 55, 67 (1998), held that the on-sale bar requires that the invention be ready for patenting. The Federal Circuit has applied the same readiness requirement to the public-use bar. Invitrogen Corp. v. Biocrest Manufacturing, L.P., 424 F.3d 1374 (Fed. Cir. 2005). Readiness can be shown by reduction to practice or by drawings sufficient to enable the invention.
Experimental use exception
Bona fide experimental use does not trigger the public-use bar. City of Elizabeth v. Pavement Co., 97 U.S. 126 (1877), upheld a patent on wooden-block paving that the inventor had tested for six years on a Boston toll road. The Court emphasized that the inventor maintained control of the testing, monitored the road's performance, and bore the costs himself. Id. at 134–35.
Factors include the necessity of public testing, who controlled the testing, whether the inventor monitored use, the duration of the test, whether confidentiality was required, whether payments were made, the inventor's intent, and the secrecy of the results. Allen Engineering Corp. v. Bartell Industries, Inc., 299 F.3d 1336 (Fed. Cir. 2002). The exception is narrow and does not protect uses primarily directed at commercial gain or market acceptance, even if testing data is also collected.
Burden and proof
The public-use bar must be proved by clear and convincing evidence. Microsoft Corp. v. i4i Limited Partnership, 564 U.S. 91 (2011). The accused infringer carries the initial burden of identifying a pre-critical-date use and showing readiness for patenting. The patentee may rebut by showing a confidentiality obligation, that the activity was experimental, or that the use did not embody the claimed invention.
Whether a use is public is a mixed question of law and fact. The underlying historical facts — who used the invention, with what restrictions, for how long — are reviewed for clear error or substantial evidence. The legal characterization of those facts as a public use is reviewed de novo. Adenta GmbH v. OrthoArm, Inc., 501 F.3d 1364 (Fed. Cir. 2007).
Like the on-sale bar, the public-use bar can be raised in district-court litigation and in post-grant review. It cannot be raised in inter partes review, which is limited to anticipation and obviousness over patents and printed publications. 35 U.S.C. § 311(b).
Interaction with related doctrines
The public-use bar's natural companion is the on-sale bar: both arise from § 102(a)(1), and a single act — for example, a commercial demonstration to potential customers — can be both a public use and an on-sale event. The two doctrines overlap in their experimental-use exceptions, which trace to a common origin in City of Elizabeth.
The public-use bar is conceptually a species of anticipation: the pre-critical-date use serves as an anticipating reference. Where a public use is asserted in the alternative as anticipating prior art, traditional anticipation principles apply, including the requirement that the prior reference disclose every limitation as arranged in the claim.
Concealment of a known pre-critical-date public use during prosecution can support an inequitable conduct defense if the use was but-for material and the patentee acted with specific intent to deceive. The Therasense standard governs.
The pre-AIA / AIA distinction is most significant for foreign uses. Pre-AIA, a public use abroad did not bar a U.S. patent (though a foreign printed publication did). Under the AIA, a foreign public use suffices, equivalent to the AIA's worldwide approach to anticipation. Patents whose effective filing date pre-dates March 16, 2013 — the AIA's effective date for first-inventor-to-file provisions — remain governed by the pre-AIA "in this country" limitation.
Practical notes
For inventors and counsel, the practical lesson of Egbert is that confidentiality must be affirmatively imposed and documented. A handshake or implicit understanding of secrecy is unlikely to suffice; a written non-disclosure agreement, marking of materials, and a documented chain of custody are the standard tools. Where third parties — beta testers, focus-group participants, contract manufacturers — encounter the invention, formal NDAs are essential.
The "no obligation of secrecy" inquiry is fact-specific. Courts look for an express obligation, a reasonable expectation rooted in the relationship (such as employer-employee), or an implicit obligation arising from the circumstances. The safest course is the express obligation; the most litigated cases involve disputed implicit obligations.
Where public testing is genuinely necessary — as in pavement, infrastructure, agricultural machinery, or medical devices that must be tested under field conditions — counsel should structure the testing under City of Elizabeth's factors: inventor control, monitoring, test purpose documented in writing, no payment beyond cost recovery, written confidentiality requirements, and limited duration. Documentation of these features at the time of testing — not reconstructed later — is critical to a successful experimental-use defense.
For litigators, public-use discovery focuses on the patentee's pre-critical-date business records: trade-show appearances, customer demonstrations, beta-test agreements, internal research notes, and FDA or other regulatory submissions in regulated industries. Depositions of pre-filing customers, demonstrators, and former employees often surface use facts that the patentee did not docket.
For accused infringers in the Eastern District of Texas, Western District of Texas, Delaware, and Northern District of California — the dominant patent fora — public-use defenses are commonly developed in parallel with anticipation and obviousness theories at the PTAB. Although the PTAB cannot adjudicate a public-use defense in IPR, evidence of pre-critical-date public use can sometimes be repositioned to support an obviousness theory based on a contemporaneous publication.
Pre-AIA versus AIA
The pre-AIA / AIA distinction continues to matter in active litigation because patents with effective filing dates before March 16, 2013, remain subject to pre-AIA § 102(b). Three differences are most important. First, the geographic scope: pre-AIA limits the bar to public use "in this country," while the AIA reaches worldwide use. Second, the inventor's grace period: under the AIA, § 102(b)(1)(A) protects only the inventor's own pre-filing disclosures, while § 102(b)(1)(B) protects against intervening disclosures derived from the inventor. Third, third-party prior use: under pre-AIA, a third-party use within the U.S. before the inventor's date of invention created prior art; under the AIA, only uses before the effective filing date count, regardless of who performed them.
Open questions
The reach of the AIA's "or otherwise available to the public" catchall is unsettled with respect to the public-use bar. Some commentators argued that the AIA narrowed "public use" to require accessibility to the public, displacing Egbert-style hidden-but-unrestricted uses. The Federal Circuit has not resolved the question definitively, but its post-AIA decisions and the Supreme Court's reasoning in Helsinn on the parallel "on sale" language suggest the historical understanding survives.
The treatment of foreign uses under the AIA continues to develop. Proof issues — gathering evidence from foreign jurisdictions, translating foreign legal concepts of confidentiality, and authenticating foreign documents — pose practical hurdles even where the substantive standard is clear.
Finally, the experimental-use exception's continued vitality after the AIA is undisputed in practice but has not been formally re-affirmed by the Supreme Court since City of Elizabeth. Federal Circuit decisions continue to apply the doctrine using the traditional factors.
See also
- On-sale barThe companion §102(a)(1) bar; public-use and on-sale events frequently overlap.
- AnticipationThe broader §102 doctrine of which the public-use bar is a species.
- ObviousnessA pre-critical-date use can also serve as a §103 reference.
- Inequitable conductConcealing a known pre-critical-date public use can support an unenforceability defense.
- Written description and enablementDistinct from but related to the "ready for patenting" prong.
- Post-grant reviewPTAB venue in which public-use challenges may be raised within nine months of issuance.
- Inter partes reviewCannot adjudicate the public-use bar; limited to printed-publication and patent prior art.
- Title 35 referenceStatutory text of §§102 and related provisions.
- GlossaryDefinitions of "critical date," "public accessibility," and "experimental use."
Last reviewed: 2026