When ‘Unique’ Means Narrow: Federal Circuit Invalidates Functionally Claimed Water Filter Patent
An ITC case invokes § 112
In a decision that serves as a poignant reminder of patent law’s core quid pro quo, the U.S. Court of Appeals for the Federal Circuit has affirmed the invalidation of a water filter patent for failing to support the full scope of its claims. The ruling highlights the risks of drafting broad, functionally defined claims that extend beyond what the specification actually teaches and demonstrates. The CAFC found that the patent’s own description of its invention as “unique” was a key piece of evidence that its inventors did not possess the broader subject matter they attempted to claim.
The case, Brita LP v. International Trade Commission, No. 2024-1098 (Fed. Cir. Oct. 15, 2025), addresses fundamental requirements of patentability under 35 U.S.C. § 112—written description and enablement—and provides critical lessons for patent prosecutors and litigators on the importance of aligning claim scope with the technical disclosure (Slip Op., p. 1). The opinion was authored by Judge Prost, joined by Judges Reyna and Chen (p. 2).
Background of the Dispute
The conflict began when Brita LP filed a complaint with the U.S. International Trade Commission (ITC) under Section 337, alleging that several companies, including the makers of LifeStraw and other filter products, were importing and selling water filters that infringed its U.S. Patent No. 8,167,141 (”the ’141 patent”) (p. 6). The ’141 patent is directed to “Gravity Flow Filter” systems that use “filter media including at least activated carbon and a lead scavenger” (p. 2).
The central feature of the invention was not a specific filter structure but a performance metric. The claims required a filter to achieve a “Filter Rate and Performance (FRAP) factor of about 350 or less” calculated by a novel formula disclosed in the patent (p. 3). This formula balanced competing performance goals like filtration speed, contaminant removal, filter volume, and lifespan.
While the patent claims broadly covered any “filter media” that could meet this FRAP factor, the specification told a much narrower story. It listed various media types, such as carbon blocks, mixed media, and membranes, suggesting the FRAP metric was “applicable to” them all (pp. 4-5). However, the patent’s own testing data and examples exclusively showed that only carbon-block filters successfully achieved the claimed FRAP value (p. 9). Conversely, the patent stated that “No mixed media filters tested met the claimed FRAP factor range due to their inability to remove particulate lead” (p. 5).
An Administrative Law Judge (ALJ) initially sided with Brita, finding a violation of Section 337. However, the full Commission reviewed and reversed this decision, determining the asserted claims were invalid for lack of written description, lack of enablement, and indefiniteness (pp. 6-7). Brita appealed this final determination to the Federal Circuit (p. 7).
The Court’s Analysis: A Specification at War with Its Claims
The Federal Circuit focused on two key legal issues: whether the ’141 patent’s specification adequately described and enabled the full scope of the claimed invention—that is, any filter media achieving the FRAP factor, not just the carbon-block type explicitly shown to work (p. 8).
The court’s analysis demonstrates how a patent’s own words can undermine its validity when the claims reach beyond the disclosed invention.
The court held that substantial evidence supported the Commission’s finding that the claims were invalid for lacking both adequate written description and enablement for non-carbon-block filters (pp. 8, 17).
In its enablement analysis, the CAFC panel leaned on the Supreme Court’s standard from Amgen Inc. v. Sanofi, reaffirming that a specification must enable a person skilled in the art to make and use the “entire class” of a claimed invention, not just a few embodiments (p. 17). The decision ultimately rested on the contrast between Brita’s broad functional claims and the narrow, specific disclosure in its patent.
The court’s reasoning was anchored in the patent’s own admissions. The specification not only failed to provide a single working example of a non-carbon-block filter meeting the claims, but it actively taught away from them (p. 9). The court found this self-contradiction fatal, quoting directly from the patent’s powerful assertion (p. 10):
“The formulations of gravity fed carbon blocks disclosed are unique in [their] ability to meet the required FRAP factor.”
The Federal Circuit found this statement, along with data showing the failure of mixed media filters, to be compelling evidence that Brita’s inventors were only in possession of a carbon-block solution (p. 10). The patent detailed the “drawbacks,” “problems,” and “disadvantages” of other filter media while extolling the specific structural and chemical properties that made its carbon-block formulations successful (p. 10).
Brita argued that because different filter media types were well-known in the “predictable art” of filtration, the specification’s detailed description of carbon blocks was sufficient to show possession of an invention applicable to all media.
The court firmly rejected this argument. It found the art was not predictable in the context of the novel FRAP equation (pp. 12, 20). Expert testimony from both sides confirmed that the variables in the FRAP formula were “all interrelated,” meaning a change to one could have an unpredictable effect on the final FRAP value (pp. 12, 16). An inventor even testified that creating a working non-carbon-block filter would require “new technology” (p. 21).
As the court explained, the specification provided no “road map” for a skilled artisan to achieve the claimed result with any media other than carbon blocks without undue experimentation (p. 18).
Key Takeaways and Practical Implications
The Brita decision offers several critical lessons for patent practitioners and innovators.
Align Claim Scope with Disclosure. Patent claims cannot be a speculative wish list for every possible embodiment of an idea. The specification must provide concrete support for the full breadth of what is claimed. Functionally claiming a result—here, a FRAP factor of 350 or less—requires a disclosure that teaches how to achieve that result across the claimed genus, not just in a single “unique” species.
A Patent’s Own Words Are Powerful Evidence. Drafters must be exceedingly careful with their language. Describing an embodiment as “unique” or detailing the failures of alternatives can be used to prove the inventor did not possess a broader invention. The specification in this case effectively fenced in the invention, providing clear evidence for invalidity that was difficult for the patentee to overcome.
Working Examples Are Crucial in Unpredictable Arts. The court emphasized that achieving the novel FRAP factor was a complex and unpredictable task. When the outcome of combining known elements is uncertain, the need for a more robust disclosure, including working examples, increases. Simply listing known filter types and stating the invention is “applicable” to them is insufficient. The specification must show how.
Functional Claims Remain Risky. This case follows the Supreme Court’s lead in Amgen v. Sanofi by scrutinizing broad, functionally defined genus claims. Practitioners who use functional language to define an invention must ensure the specification provides either a representative number of species that meet the function or identifies common structural features that allow a skilled person to recognize all members of the genus (p. 14). The ‘141 patent did neither.
Conclusion
The Federal Circuit’s decision in Brita v. ITC is a straightforward but essential reaffirmation of the patent bargain: in exchange for a limited monopoly, an inventor must fully describe and enable their invention for the public.
The ruling serves as a cautionary tale against aggressive claim drafting that outpaces the underlying science. It underscores that for patent claims to be valid, the specification must provide a credible guide to the full territory claimed, not just a detailed map of one successful corner of it.
For patent drafters, the message is clear: show, don’t just tell, and be wary of describing an invention so narrowly that its “uniqueness” becomes its downfall.
Disclaimer: This is provided for informational purposes only and does not constitute legal or financial advice. To the extent there are any opinions in this article, they are the author’s alone and do not represent the beliefs of his firm or clients. The strategies expressed are purely speculation based on publicly available information. The information expressed is subject to change at any time and should be checked for completeness, accuracy and current applicability. For advice, consult a suitably licensed attorney and/or patent professional.