Mitsui Chemicals v Borealis (EPO, G 1/23, 2025)

Dhenne Avocats · 11 October 2026

Our analysis

Summary

The Enlarged Board of Appeal held that a product put on the market before the filing date cannot be excluded from the state of the art within Article 54(2) EPC for the sole reason that its composition or internal structure could not be analysed and reproduced by the skilled person. Technical information made available to the public about that product also forms part of the state of the art, irrespective of that possibility. The decision abandons the reproducibility condition derived from opinion G 1/92 and leaves the effect of non-reproducible properties to the assessment of novelty and inventive step.

Facts and procedure

Mitsui Chemicals, Inc. and Mitsui Chemicals ICT Materia, Inc. held EP 2 626 911, concerning an encapsulating material for solar cells. After the Opposition Division rejected the opposition filed by Borealis GmbH, the opponent appealed. The closest prior art was the commercial product ENGAGE® 8400, a complex polymer whose manufacturing method was not public and whose exact reproduction was not straightforward. The proprietor argued that this non-reproducible product was not part of the state of the art in the light of G 1/92. In T 438/19 of 27 June 2023, Technical Board of Appeal 3.3.03 referred three questions.

The applicable law

Article 54(2) EPC defines the state of the art as everything made available to the public before the date of filing; that concept also governs Article 56 EPC. Under opinion G 1/92, the chemical composition of a product is state of the art when the product is available to the public and can be analysed and reproduced by the skilled person, irrespective of any particular reason for analysing it (point 7).

Question

Must a product put on the market before the filing date be excluded from the state of the art for the sole reason that its composition or internal structure could not be analysed and reproduced without undue burden by the skilled person?

Decision

A product put on the market covers both man-made products and naturally occurring materials (point 30). Reproduction means physical reproduction, by a route other than buying the product, on the basis of common general knowledge alone (points 31, 38 and 39).

The first reading of G 1/92, excluding the product in its entirety, rests on a legal fiction contrary to experience (point 48). It leads to an absurd result: since common general knowledge cannot exceed the state of the art, and every material ultimately depends on non-reproducible starting materials, no material would belong to the state of the art, which would become an empty set (points 51, 60, 63 and 65). The second reading, excluding only the composition, is also rejected (point 70); both interpretations lead to a manifestly absurd result (point 72). The reproducibility condition is therefore redundant: the chemical composition of a product is part of the state of the art when the product is available to the public and can be analysed by the skilled person (point 73). All analysable properties of the product form part of it, and a later product cannot be novel if all the claimed features were disclosed by the earlier product (points 74 and 75). Whether analysis must be possible without undue burden was left open (points 78 and 79).

Later disappearance or modification of the product is a matter of proof and does not deprive it of prior art status (points 84, 85 and 88). For novelty the product cannot be ignored, as with an accidental anticipation (point 94); for inventive step, the weight of non-reproducible properties depends on the circumstances, and such a product may be the closest prior art (points 95 and 96). Publicly available technical information about the product is state of the art (point 98), and the third question was moot (point 100).

Key points for practice

• A product marketed before the filing date is state of the art even if its composition cannot be reproduced (point 80).
• All analysable properties of such a product may be cited against novelty (points 74 and 75).
• The effect of non-reproducible properties on inventive step is assessed case by case (points 95 and 96).
• Practical point: document promptly, through dated analyses and samples, the properties of a competing marketed product, since its later disappearance raises only a question of proof (points 84 to 86).

Provisions applied

European Patent Convention

Art. 54(2), 56, 83, 112(1), 117(1)(f)

Other instruments

Rules of Procedure of the Enlarged Board of Appeal, Arts 9 and 10

Case law cited

G 2/88; G 6/88; G 1/92; G 2/03; G 1/11; G 4/19; T 206/83; T 952/92; T 1553/06; T 23/11; T 1833/14; T 438/19

Prepared by Dhenne Avocats from the text of the decision (epo.org, official English text), consulted on 11 October 2026. Only the official text is authoritative.