Understanding The “Public Use”​ Deadline For Patent Protection
David M. Kleiman – U.S. Patent Attorney

To obtain exclusive legal rights in an invention through a patent the inventor must disclose the invention to the government before certain events happen. In the United States one such event is the invention being in “public use”.

The general rule is that if an invention is in “public use” before a patent application is filed, then patent protection for the invention will not be available. This is commonly referred to as a “public use” bar to patent protection. To know whether a “public use” bar applies one has to know when an invention was first in “public use”, and by who.


The date that an invention is in “public use” under U.S. patent law is the date:

  1. The invention is ready for patenting; AND
  2. A use is made of the invention that is either:
    1. Accessible to the public; OR
    2. A commercial exploitation of the invention.
When Is An Invention “Ready for Patenting”?

This is the same as for the “on sale” bar written about in a prior article: Under U.S. patent law an invention is considered ready for patenting when the invention is actually reduced to practice or the inventor has prepared drawings or other descriptions of the invention that are sufficiently specific to enable a person skilled in the art to practice the invention.

Actual Reduction To Practice

An invention is actually reduced to practice when it has been constructed (or if a process, then performed) and has successfully worked for its intended purpose. Note that what has been actually constructed or performed need not be a final commercial embodiment or implementation of the invention. Even a rough laboratory prototype that works will suffice and be considered “ready for patenting”.

Drawings or Descriptions

But as mentioned above, to be “ready for patenting” does not require actual reduction to practice of the invention. If drawings or other descriptions of the invention are prepared that are sufficiently specific to enable a person skilled in the art to practice the invention, then it will be considered to be “ready for patenting”. This is why filing a patent application which contains such drawings or other description is considered a “constructive” reduction to practice. However, the drawings or descriptions do not need to be in a patent application. Drawings or descriptions internal to a business, or those given to a third-party manufacturing facility, will satisfy the “ready for patenting” requirement if they are sufficiently specific to enable a person skilled in the art to practice the invention.

When Is The Use Of An Invention Accessible To The Public?

Courts consider a number of factors to determine whether use of an invention was “accessible to the public”. Perhaps the most significant factor in the determination is whether the use of the invention had been subject to any limitation or restriction, or injunction of secrecy.

For example, in the seminal Supreme Court case of Egbert v. Lippmann it was decided that a corset-spring invention sewn into a corset had been publicly used by the inventor’s wife when she used the corset as an undergarment for many years before a patent application was filed. This was so despite the fact that her personal use of the invention with an undergarment was “private” and invisible to the public.

A key factor for the court in that case was that the inventor had not imposed any limitation or restriction, or requirement of secrecy, on his wife’s use of the invention. Accordingly, the use was a “public” use even though the invention was not visible or available to the public.

Accordingly, as a general precautionary rule, to prevent the use of an invention from being considered “accessible to the public”, anyone involved in the use of an invention before a patent application is filed should execute a written agreement restricting their use of the invention and obligating them to keep it secret.

When Is The Use Of An Invention A Commercial Exploitation?

There can be instances in which a secret or confidential use of an invention will nonetheless still be considered to be a “public use” of the invention.

Under U.S. patent law it is a condition upon an inventor’s right to a patent that he shall not exploit his discovery competitively after it is ready for patenting: An inventor must be satisfied with either protecting the invention as a trade secret or seeking the exclusivity offered by patent protection. Thus, even if an inventor imposes limitations and obligations of secrecy on the use of an invention, any use of the invention that is a “commercial exploitation” of the invention after it is ready for patenting will be deemed a public use preventing patent protection.

A “commercial exploitation” of an invention can be something other than “commercial offer for sale” of the invention: Otherwise, there would be no difference between the “public use” and “on sale” bars to patentability, and these two bars to patentability are set forth in the law as being separate and distinct. Accordingly, an inventor can be found to have “commercially exploited” an invention without having actually commercially offered the invention for sale. So, the question then becomes what activity other than a “commercial offer for sale” of the invention will be considered a use that is a “commercial exploitation” of the invention?

The Supreme Court in the 1878 case of Elizabeth v. Pavement stated that “any attempt to use [an invention] for a profit, and not by way of experiment. . .” will be a public use depriving an inventor of the right to a patent if a patent application has not already been filed. Accordingly, the “commercial exploitation” issue has generally been addressed by the courts as a determination of whether a use which was not “accessible to the public” was an “experimental use”, with the rule being that if a use is an “experimental use” then it is not a “public use”. Otherwise, if a use is not experimental and is related to making a profit, then it may be found to be a “commercial exploitation” of the invention.

What Is an Experimental Use of An Invention?

As stated, an experimental use of an invention is not a “public use” for purposes of patent protection. However, a use will only be considered experimental if at the time of the use an objective evaluation of the facts shows that the primary purpose of the use was to conduct experimentation. Experimentation must be the primary purpose and any commercial exploitation must be incidental. In determining whether the primary purpose for a use of the invention is experimental courts may consider a number of factors:

  • The necessity for public testing.
  • The amount of control over the experiment retained by the inventor.
  • The nature of the invention.
  • The length of the test period.
  • Whether payment was made.
  • Whether there was a secrecy obligation.
  • Whether records of the experiment were kept.
  • Who conducted the experiment.
  • The degree of commercial exploitation during testing.
  • Whether the invention reasonably requires evaluation under actual conditions of use.
  • Whether testing was systematically performed.
  • Whether the inventor continually monitored the invention during testing.
  • The nature of contacts made with potential customers.

A use should be found by a court to be experimental if it represents a bona fide effort to perfect the invention or to ascertain whether it will work for its intended purpose. If any commercial exploitation does occur, it must be merely incidental to the primary purpose of the experimentation to perfect the invention.

It is important to be aware that courts have held that market testing by an inventor to gauge consumer demand for an invention is a commercial exploitation and is not experimentation for purposes of the “public use” bar to patentability.

Accordingly, to minimize the risk of a court concluding that a use of the invention before a patent application was filed was a “commercial exploitation” of the invention, an inventor should document and evidence the primary experimental purpose of any such uses. This means clearly documenting, and ideally maintaining corroborating evidence, showing that the purpose of any use before a patent application was filed was primarily to perfect the invention or establish that the invention worked for its intended purpose.


As stated, the general rule is that an invention is not eligible for patent protection unless a patent application has been filed before the invention is in “public use”. In the United States there is a limited exception to this rule: If the invention was in “public use” by the inventor, or in “public use” by another who had obtained the invention from the inventor, then U.S. patent protection can still be applied for up to one year after the “public use” date.

However, being able to take advantage of this limited exception may require an applicant for U.S. patent protection to submit evidence that an alleged “public use” of the invention before the application filing date was by the inventor or someone who obtained the invention from the inventor. Accordingly, to the extent a business chooses to delay filing a patent application after the “public use” date of an invention, it is important that the business maintain adequate documentation of any uses of the invention by it, and of all parties who the business disclosed the invention to.

It is also important to know that the same exception does not necessarily apply outside of the United States: An invention being in “public use” before a patent application is filed can prevent foreign patent protection.


A business that wants to have exclusive rights in an invention should preferably file a patent application as soon as an invention is “ready for patenting” and before the “public use” date of the invention. All uses of the invention by any persons before a patent application is filed should be subject to appropriate confidentiality agreements, and the primary purpose of all such uses should be carefully documented and corroborated.

If the filing of a patent application is delayed until after the “public use” date, then the delay should be minimized, with documentation and corroborating evidence maintained which can establish that the “public use” of the invention was by the inventor, or by one who obtained it from the inventor. Under no circumstances can a U.S. patent be obtained on an invention that has been in “public use” for more than a year.