On-Sale Bar Doctrine brought closer to United States by EPO Enlarged Board of Appeal

On-Sale Bar Doctrine brought closer to United States by EPO Enlarged Board of Appeal

The update recaps the background of G 1/23 and main findings of the decision; underscores significant differences between the European and US on-sale bar; and defines practical takeaways for patent practitioners.

The Enlarged Board of Appeal (EBA) of the European Patent Office (EPO) in G 1/23 in its July 2, 2025 decision introduced a change in European patent law’s treatment of publicly available products, especially where their composition is not fully disclosed or reproducible.

G 1/23 remodels the boundaries of what constitutes prior art under the European Patent Convention and affects how publicly available products, product descriptions and marketing materials are assessed in determining novelty and inventive step, thereby having broad implications for patent practitioners across all technical fields. The decision brings Europe closer to the United States’ on-sale bar doctrine but significant differences remain. The update recaps the background of G 1/23 and main findings of the decision; underscores significant differences between the European and US on-sale bar; and defines practical takeaways for patent practitioners.

After the earlier EBA G 1/92 decision, the existing understanding was that for a product made available to the public (for example, a product sold on the market) to be considered part of the prior art, it had to be both analyzable and reproducible by the skilled person. Practically, this meant that if the internal composition or structure of a product was too complex or obscured to be reverse engineered without undue burden, it might not qualify as prior art, even if it was commercially available. This interpretation is overruled by G 1/23. Once a product is available for public inspection or use, it becomes part of the state of the art and any technical information that is derivable from it such as its measurable or observable properties must also be considered in novelty and inventive step assessments, the EBA held.

The patent at issue (EP 2 626 911) involves a compressing material for solar cell modules. For the polymeric composition defined by Claim 1, ENGAGE® 8400, a Dow (third party) manufactured ethylene/olefin copolymer, was cited as the closest prior art. Available on the market before the patent’s filing date, this polymer had technical properties corresponding to that of the claimed invention except for one feature – a residual aluminium content of approximately 4.4 ppm, which is below the claimed minimum of 10 ppm.

The basic properties and intended applications of ENGAGE 8400 were publicly documented but its precise composition and manufacturing process were not disclosed and could not be straightforwardly reproduced. Because the skilled person could not reproduce the product’s internal structure, it should be excluded from the prior art under Article 54(2) EPC, the patentee argued. The view was rejected by the Enlarged Board which reasoned that excluding such products would lead to an unsustainable legal fiction that is, treating a well-known, widely used product as if it had never existed from the perspective of the skilled person.

Thus, it no longer matters whether the skilled person could have discovered how to make the product and public accessibility alone is determinative. To sum it up, the analysis under Article 54(2) EPC is reoriented toward what the public has access to, not what the skilled person could technically reproduce by G 1/23.

In the United States, 35 U.S.C. §102 bars the grant of a patent if the claimed invention was “on sale” before the critical date, which is defined as one year prior to the effective filing date of the patent application. There are important differences between Europe and the United States in the scope and application of the on-sale bar. Even confidential or secret sales may trigger the bar under US law whereas only public availability counts under the EPC.

Europe does not offer a general grace period except for limited exceptions under Article 55(1)(a) EPC like disclosures due to abuse or at official exhibitions while the United States provides a one-year grace period under 35 U.S.C. §102(b). In the United States, experimental use may avoid the on-sale bar if the purpose is to test the invention’s functionality. In Europe, experimental use may avoid creating prior art only if it occurs under conditions of confidentiality or control. These differences can lead to divergent outcomes for similar fact patterns and must be considered when developing global patent strategies.

The impact of G 1/23 extends to all fields of technology although G 1/23 arose from a case in polymer chemistry. The Enlarged Board itself noted that the question of reproducible prior use can arise in any area involving complex products. By effectively broadening what counts as prior art, G 1/23 will influence how novelty and inventive step are evaluated across the board. Patent practitioners should be aware of key implications such as:

• No safe harbor for secret know-how once product is public: Pre-G 1/23, some applicants might have assumed that if they kept their manufacturing process or composition details secret, they could market a product and later seek a patent on it (or on its properties) so long as competitors couldn’t readily reproduce it. This strategy is now untenable. Any non-confidential sale or public use of a product before the filing date will count against novelty or inventive step of that same product in Europe.
• Public disclosures of product information are fully prior art: Companies often publish data sheets, white papers, or brochures describing features of their products. G 1/23 makes clear that any technical information disseminated about a product is part of the state of the art. Even if certain internal aspects are not disclosed, whatever is disclosed (or can be measured from the product) will be considered known to the public.
• Relevance in high-tech and ‘black box’ scenarios: The decision is especially significant for fields like pharmaceuticals, biotechnology, electronics, or software, where marketed products may contain undisclosed but functionally observable innovations.
• Focus on evidence: The Enlarged Board’s approach shifts the debate to proof of properties. If a prior product potentially anticipates or renders an invention obvious, the discussion will turn on whether the opponent has adequate evidence of the product’s relevant features.
• Inventive step analysis: While G 1/23 closes the door on patenting an identical product that was previously available, it does not preclude patents on improvements or modifications. For example, while ENGAGE® 8400 was the closest prior art, the claimed higher aluminum content was not in the product. The key question is whether a skilled person would have found it obvious to adjust the aluminium content to the claimed range, thereby achieving the improved properties.
• Leverage prior uses in oppositions/litigation: If opposing a patent or defending against one, consider whether any prior product sales or uses can serve as invalidating prior art. Be prepared with evidence such as lab analyses, affidavits, and dated product literature.

Patents granted under the now-rejected G 1/92 framework may face increased vulnerability. Practitioners should re-evaluate such cases in light of G 1/23.