What Is a Patent File Wrapper?

By Lisa Magloff

A patent is a grant made by the United States Patent and Trademark Office that gives inventors and creators exclusive rights to sell and license their inventions. A patent creates an ownership right in intellectual property. The patent application process, also known as the patent prosecution, is a lengthy administrative process requiring the creation and filing of a large number of documents, which are contained in a file wrapper. The contents of the file wrapper may serve an important legal function in the event of a dispute over the patent.


The patent file wrapper is an electronic or paper folder that contains all of the documents pertaining to a particular patent application. It is a complete record of the application, including all of the documents relating to the patent such as diagrams and drawings; communications between the United States Patent and Trademark Office and the applicant; statements made by the applicant; and records of official actions by the USPTO. The wrapper may also contain records of interviews of the applicant conducted by the USPTO. Since 2003, all file wrappers are stored electronically, but patents granted before this date may still have hard-copy wrappers.


The file wrapper provides a complete legal record of the patent application. This information can be crucial in the event of a lawsuit over patent infringement because only the information contained in the file wrapper can be used to demonstrate the nature of the invention, the precise time the patent was requested and granted, and the scope of the patent. Information in the file wrapper is in the public domain and can be examined by anyone who requests it.

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Role in Estoppel

The legal doctrine of file wrapper estoppel is an important one in patent law. The effect of estoppel is to bind the applicant to any statements he made during the application process that are held in the file wrapper. The applicant is prevented or "estopped" from later claiming that his statements meant something different. It often happens that the USPTO will deny a patent on the basis that it is too similar to an existing patented invention. In such a case, the applicant can appeal the decision by attempting to narrow the scope of the patent to distinguish this invention from the other, similar one. But, under the doctrine of estoppel, the applicant cannot alter any statements or claims previously made about the scope of the invention that are contained in the wrapper. During a legal dispute over denial of a patent, the USPTO will examine the file wrapper to determine if estoppel applies.

Trade Secrets

At times, the applicant for a patent may need to submit information to the government that is proprietary or is a trade secret. Because the file wrapper is available to the public, this may cause problems for the applicant. In order to prevent people from stealing trade secrets contained in the file wrapper, the USPTO labels proprietary information as “not to be opened by the public," and removes these documents from the file wrapper prior to forwarding it to the person making the request.

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