What is the public use bar in patent law?
The public use bar is a patent law doctrine that prevents an inventor from obtaining a patent on an invention that was in public use before the statutory cutoff date tied to the application's effective filing date. The bar can attach even when the use involved only one person and was never publicly disclosed.
Statutory basis
Under AIA 35 U.S.C. § 102(a)(1), a claimed invention is not patentable if it was "in public use" before the effective filing date. Public use is one of several prior art categories in that clause, alongside patents, printed publications, sales, and subject matter "otherwise available to the public."
What constitutes a public use
Pre-AIA case law identified two categories of prior use that constitute a public use bar: (1) a use that was accessible to the public, or (2) a use that was commercially exploited by the inventor. Under the AIA, however, the public use bar is expressly limited to uses that are accessible to the public.
The distinction matters when analyzing third-party uses. A prior use by a third party who did not obtain the invention from the inventor is an invalidating public use under AIA § 102(a)(1) only if that use was accessible to the public; secret commercial exploitation by an independent third party does not independently constitute a public use bar under the AIA.
The rule was broader for inventor-originated uses under pre-AIA law. Under pre-AIA 35 U.S.C. § 102(b), an inventor's own prior commercial use of the invention, even if kept completely secret, constituted a public use barring patentability. Practitioners handling applications with pre-AIA effective filing dates must apply this broader standard rather than the AIA's accessibility-focused approach.
Egbert v. Lippmann: the foundational case
The leading authority on what makes a use "public" is Egbert v. Lippmann, a Supreme Court decision from 1881. The Supreme Court in Egbert v. Lippmann held that giving an invention to another person for unrestricted use, without imposing any obligation of secrecy or condition of restriction, constitutes a public use that bars patentability, even if only one person uses the invention (in that case, two corset springs worn under clothing by a single individual for several years).
The hidden nature of the invention did not save the patent: the Supreme Court in Egbert v. Lippmann held that an invention hidden from general view during use can still constitute a public use, because the inventor imposed no secrecy obligation on the recipient, leaving her free to exhibit the springs or replicate them.
What makes a use "public" under Egbert is not the number of observers or the visibility of the disclosure. The decisive factor is whether the inventor imposed any restriction on the recipient's ability to share, copy, or further disclose the invention. A single, private, fully-concealed use by one person is sufficient to trigger the bar if no enforceable restriction was imposed on the recipient.
AIA vs. pre-AIA: key differences
Geographic scope
The AIA significantly broadened the geographic reach of the public use bar. Under the AIA, there is no geographic limitation on where a prior public use may occur; a public use anywhere in the world before the effective filing date can bar patentability. Under pre-AIA 35 U.S.C. § 102(b), the public use bar applied only to public use occurring in the United States.
Applications governed by pre-AIA § 102(b) benefit from the domestic geographic limit. AIA applications face worldwide exposure. Confirm which regime governs before advising on any pre-filing use, particularly for inventors with international commercial activity.
Inventor's own secret use
As noted above, the AIA narrowed the scope of the public use bar for inventor-originated secret uses relative to pre-AIA law. Under pre-AIA, an inventor's own secret commercial exploitation was independently barring. Under the AIA, the public use bar is limited to uses accessible to the public. A secret commercial arrangement by the inventor may still implicate the on-sale bar or the "otherwise available to the public" catchall in the same AIA § 102(a)(1) clause.
Experimental use exception
Not every use before the filing date is barring. The experimental use exception is the most significant carve-out from the public use bar.
The exception applies when the primary purpose of the inventor at the time of the use, as determined from an objective evaluation of the facts, was to conduct experimentation, with any commercial activity being merely incidental.
When sales are made in an ordinary commercial environment and the goods are placed outside the inventor's control, an inventor's secretly held subjective intent to experiment, even if true, is unavailing without objective evidence to support the contention. In practice, an inventor who keeps no records and exercises no control over the use will struggle to prove the activity was experimental rather than public.
Market testing falls clearly outside the exception. A use where the inventor is attempting to gauge consumer demand for the invention rather than evaluate its technical function does not qualify as experimental use and constitutes a barring public use.
Courts assess thirteen factors when evaluating whether a use was experimental, including: (1) the necessity for public testing, (2) the amount of control over the experiment retained by the inventor, (3) the nature of the invention, (4) the length of the test period, (5) whether payment was made, (6) whether there was a secrecy obligation, (7) whether records were kept, (8) who conducted the experiment, (9) the degree of commercial exploitation during testing, (10) whether the invention reasonably requires evaluation under actual conditions of use, (11) whether testing was systematically performed, (12) whether the inventor continually monitored the invention during testing, and (13) the nature of contacts made with potential customers.
The experimental use exception is personal to the inventor; when third parties conduct alleged experimental activity without inventor supervision and control, the inventor cannot rely on that activity to invoke the exception.
Grace period exception
The AIA provides a grace period that can shelter the inventor's own pre-filing public use. Under AIA 35 U.S.C. § 102(b)(1)(A), a public use by the inventor or joint inventor, or by another who obtained the subject matter directly or indirectly from the inventor, within the statutory period before the effective filing date, is excepted from the public use bar and does not constitute prior art.
The exception has a hard traceability limit: the AIA grace period exception does not apply to an independent third-party public use; a use by a party who independently obtained the subject matter, not from the inventor, is not sheltered by the grace period exception. If a third party independently developed the same invention and publicly used it before the grace period window opened, the inventor has no AIA mechanism to neutralize that prior use under the public use bar.
Practical notes for practitioners
| Scenario | Public use bar risk |
|---|---|
| Product demonstrated at a trade show before filing | High: accessible to the public |
| Invention used internally in the inventor's lab, never shown outside | Low under AIA: not accessible to the public |
| Invention given to a colleague with verbal confidentiality request, no written obligation | Elevated: verbal request may not constitute an enforceable restriction under Egbert |
| Invention given to a colleague under a signed NDA with written use restriction | Lower: written restriction establishes secrecy obligation that may negate Egbert analysis |
| Field test with written protocol, documented monitoring, secrecy agreements, and no payment | Lower: experimental use exception may apply if well-documented |
| Survey of potential customers where the product is shown and demand gauged | High: market testing; not experimental use |
- Treat unrestricted disclosure as public use. Under Egbert, giving one person an unrestricted copy or access is enough. If the recipient is not bound by a written, enforceable secrecy or restriction obligation, the disclosure is likely a public use regardless of what the inventor intended.
- Written secrecy obligations matter more than verbal ones. The Egbert bar turns on whether the inventor imposed a restriction on the recipient. A signed NDA or written restriction is the clearest way to establish that restriction. Verbal confidentiality requests are harder to prove and more vulnerable to challenge.
- Document the experimental protocol before the test begins. If the experimental use exception may be at issue, build a contemporaneous record before the test starts: the written hypothesis, the specific function being evaluated, monitoring logs, written instructions to participants about the experimental nature of the activity, and documentation of what was done with results. After-the-fact characterization of a use as experimental is difficult to sustain without this record.
- Distinguish technical testing from market testing. Evaluating whether the invention works as intended is experimental use. Showing the invention to potential customers to gauge interest or demand is market testing and falls outside the exception, regardless of the inventor's subjective intent.
- Verify AIA vs. pre-AIA governing dates. For applications with pre-AIA effective filing dates, the inventor's own secret commercial use may constitute a public use bar, and the geographic scope is limited to U.S. activity. The analysis differs materially from AIA cases.
- An independent third-party public use before the grace period window cannot be excepted. If a third party independently used the invention publicly before the grace period window opened, the inventor has no AIA statutory mechanism to neutralize that prior use under the public use bar.