Many U.S. patent applicants have never given much thought to the “best mode” requirement. That’s understandable. While U.S. patent law still technically requires inventors to disclose the best way of practicing their invention, Congress removed the penalty for failing to do so more than a decade ago.
Australia just reminded everyone that not every country is so forgiving.
A recent Australian appellate decision, The NOCO Company v. Brown and Watson International Pty Ltd [2026] FCAFC 44, reinforces an important point for companies seeking international patent protection: a disclosure strategy that works in the United States may create serious validity problems abroad.
What Is the Best Mode Requirement?
The best mode requirement is simple in concept.
If an inventor knows a preferred way of carrying out the invention, the patent application must disclose it. The idea is that inventors should not receive a patent monopoly while secretly withholding the most effective version of their invention from the public.
Suppose an inventor develops a chemical process that works with ten possible catalysts but knows that Catalyst X consistently produces better results. Under a best mode requirement, merely listing all ten catalysts may not be enough. The inventor may be required to disclose that Catalyst X is the preferred approach.
Historically, the United States imposed this requirement as part of the bargain underlying the patent system: exclusive rights in exchange for full disclosure.
The Curious State of U.S. Law
The United States still has a best mode requirement on the books.
35 U.S.C. §112 requires a patent specification to “set forth the best mode contemplated by the inventor” for carrying out the invention. However, the America Invents Act (AIA) dramatically weakened the requirement in 2011. Failure to disclose best mode can no longer be used to invalidate a patent or render it unenforceable.
As a practical matter, many practitioners view best mode as largely toothless. Even if an applicant omits its preferred embodiment, an accused infringer generally cannot attack the patent on that basis.
That creates a temptation. Why disclose proprietary manufacturing preferences, optimized settings, or preferred materials if there is no meaningful penalty for withholding them?
The answer is that foreign patent offices may take a very different view.
Australia Still Means It
Australia remains one of the few major patent jurisdictions that actively enforces a best method requirement.
Australian patent law requires a complete specification to disclose the best method known to the applicant for performing the invention. Unlike the United States, failure to satisfy this requirement can be raised during opposition proceedings, reexamination proceedings, and patent revocation actions.
As a result, challengers increasingly rely on best method attacks when attempting to invalidate Australian patents.
The NOCO Decision Raises the Stakes
The recent Australian decision involved divisional patent applications.
A divisional application is a later-filed patent application that claims subject matter from an earlier parent application. Divisional applications are common in both the United States and Australia.
The key question was straightforward: When evaluating best method compliance for a divisional application, should courts look at the best method known when the original parent application was filed, or the best method known when the divisional application itself was filed? Australia’s Full Federal Court chose the latter.
The court held that a divisional application must disclose the best method known to the applicant at the filing date of the divisional application itself. If the applicant learned a better way of practicing the invention after filing the parent application but before filing the divisional, that improved method may need to be disclosed in the divisional specification.
That can create a significant challenge for patent owners. Divisional applications are often filed years after the original application. During that time, inventors may continue refining products, manufacturing processes, formulations, software implementations, or operating parameters.
Under the NOCO decision, those later-developed improvements may become relevant to best method compliance.
Why U.S. Applicants Should Care
Many U.S. patent applications are drafted with the assumption that best mode challenges are effectively off the table. That assumption may be harmless if protection is sought only in the United States. It becomes much riskier when the same patent family is filed internationally.
An application that omits preferred manufacturing techniques, preferred materials, optimized process conditions, or other known “best” approaches may survive scrutiny in the United States. The same omission could become a validity issue in Australia.
The risk may be particularly acute for divisional applications filed years after the original application, when the applicant’s understanding of the invention has evolved.
Australia Is Not Alone
Australia is not the only country that continues to require disclosure of the applicant’s best way of performing an invention.
India expressly requires a patent specification to disclose “the best method of performing the invention which is known to the applicant.” Failure to satisfy that requirement can create validity problems and may support revocation of a granted patent.
New Zealand likewise requires a complete specification to disclose “the best method of performing the invention” known to the applicant. The requirement is built directly into the Patents Act 2013 and forms part of the disclosure obligations imposed on patent applicants.
The United States is therefore something of an outlier. While U.S. law still contains a best mode requirement, Congress eliminated best mode as a basis for invalidating or rendering a patent unenforceable. As a result, a disclosure strategy that may present little practical risk in the United States could create significant issues in countries where the requirement remains enforceable.
The Practical Takeaway
For companies pursuing international patent protection, especially in Australia, disclosure decisions made during U.S. patent drafting can have consequences years later.
The safest course is often the simplest one: if the inventors know the best way to practice the invention, disclose it. That approach may seem unnecessary in the United States, where best mode is rarely litigated. But overseas, particularly in Australia, a failure to disclose the best method can still provide a potent weapon for patent challengers. The NOCO decision serves as a reminder that a patent strategy built solely around U.S. law can create unexpected vulnerabilities once the application crosses international borders.