Indefinite claims can render a patent invalid. PACIFIC COAST v. CERTAINTEED

A patent is a set of exclusive rights granted to an inventor for an invention. The public policy for granting patents is to encourage the sharing of knowledge. Inventors that apply for, and are granted a patent, are rewarded for sharing their knowledge with the public. Inventors are rewarded with a monopoly on the invention for a limited period of time. In exchange for that monopoly inventors must teach the public all the details about an invention.

A patent is a complicated document with several different sections. The claims of a patent are like property lines on a map. Elements of an invention can be described in the specification section of the patent, but if those elements are not claimed then the patent does not cover those elements. All patent specifications shall conclude with one or more claims particularly pointing out and distinctly claiming the subject matter which the inventor or a joint inventor regards as the invention. 35 U.S.C. § 112(b). The claim language must be “definite” to comply with 35 U.S.C. 112(b).

A patent claim is indefinite if it fails to inform a person having ordinary skill in the art about the scope of the invention, with reasonable certainty. Reasonable certainty does not require absolute or mathematical precision. However case precedent has found patent claims to be indefinite when there is more than one way to measure a physical characteristic and the patent specification does not disclose how the inventor is measuring. The primary purpose of this requirement of definiteness of claim language is to ensure that the scope of the claims is clear so the public is informed of the boundaries of what constitutes infringement of the patent.

Normally the United States Patent and Trademark Office will refuse to issue a patent when a patent claim is indefinite. The inventor will be required to amend the patent application to provide enough information so that the enablement requirement is satisfied. But sometimes the United States Patent and Trademark Office misses something and a patent gets issued which does not fulfill the definiteness requirement of 35 U.S.C. 112(b).

PACIFIC COAST BUILDING PRODUCTS, INC., v. CERTAINTEED GYPSUM, INC., 19-1524 (C.A.F.C. 2020) is an example of a case where a patent was invalided because the claims did not meet the “definite” requirement of 35 U.S.C. 112(b).

Plaintiff in this case owns U.S. Patent No. 9,388,568 (the ’568 patent) which is directed to Acoustical sound proofing material with improved fracture characteristics. Claim 21 of the ’568 patent is directed to a drywall structure having a “scored flexural strength” of “about 22 pounds per 1/2 inch thickness of the structure.” Plaintiff sued Defendant for infringement of the patent.

The District Court found that there are multiple ways to measure “scored flexural strength” and that the specification’s lack of guidance for choosing which measurement to use renders claim 21 indefinite. Plaintiff appealed the district court’s claim order, which found the claim term “scored flexural strength” indefinite to the Court of Appeals for the Federal Circuit.

The Fedederal Circuit found no clear error by the District Court and affirmed the ruling. The Federal Circuit noted that the claims recite a particular value for “scored flexural strength,” i.e., “about 22 pounds per 1/2 inch thickness,” but the claims and specification fail to explain what the value represents or how to consistently and reproducibly measure this new characteristic. Because the patent fails to explain how “scored flexural strength” should be measured, and because a skilled artisan would have had no reasonable certainty to figure out how to calculate “scored flexural strength”, the Federal Circuit agreed that the claim was indefinite under 35 U.S.C. 112(b).

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