January 2026 This UPC Court of Appeal’s decision in Otec v. Steros provides further guidance on how claims are to be interpreted at the UPC. The Court made it clear that experimental data produced after the filing of a patent application and not disclosed in a patent specification generally cannot be used to clarify the meaning of the claims and can only be relied upon in exceptional circumstances. The ruling underscores the importance of drafting claims and descriptions that are clear and complete from the outset.
Background
The UPC Court of Appeal’s decision in Otec v. Steros provides an interesting insight into claim interpretation and the constraints on relying on post-filing experimental evidence at the UPC. The case, UPC Court of Appeal decision 579/2025, arose from a first instance decision from the Hamburg Local Division (LD) in which a preliminary injunction was granted the against Otec in June 2025, based on Steros’ European patent EP 4249647.
For context, EP 4249647 concerns compositions suitable for use in electropolishing. Claim 1 describes an electrolytic medium comprising two key components:
- i) solid electrolyte particles containing a conductive solution with an electrical conductivity above 10 µS/cm, and
- ii) a non-conductive, immiscible fluid that does not form a single phase with the conductive solution.
The key point of contention in both the first instance decision and the Court of Appeal decision, was how to interpret the “non-conductive fluid” feature required by claim 1, as the application does not numerically define what is meant by the term “non-conductive”.
The alleged infringement by Otec involved an emulsion in which solid particles were added to a medium, creating a system with droplets of one liquid dispersed in another continuous phase.
At first instance, because there was an absence of explicit numerical guidance on what “non-conductive” meant in EP 4249647, the Hamburg LD interpreted that the only numerical benchmark in the claim (i.e. the 10 µS/cm conductivity value given for the conductive solution) should function as an upper limit. It was deemed that if the “conductive solution” must have a conductivity greater than 10 µS/cm, then the conductivity of the “non-conductive fluid” must reasonably be below that value.
Steros submitted experimental data in which the phases of the Otec’s emulsion were separated and the conductivity of the oil phase was measured at 0.291 µS/cm, well below the 10 µS/cm threshold, while the non-oil phase possessed a conductivity above 10 µS/cm.
On this basis, the LD found a likelihood of both validity and infringement of EP 4249647 and granted a preliminary injunction against Otec.
The Court of Appeal Decision
The Court of Appeal agreed with some of the LD’s reasoning. For instance, the court confirmed that, in the absence of further guidance in EP 4249647, interpreting “non-conductive fluid” as having a conductivity below 10 µS/cm was reasonable.
However, Court of Appeal diverged on a key point. The Court of Appeal disagreed with the LD’s method of measuring conductivity by isolating a single phase of the emulsion.
The Court noted that EP 4249647 allowed the non-conductive fluid itself to be an emulsion, meaning conductivity should be assessed for the overall emulsion as supplied and used. When this approach was applied to the alleged infringing product, the conductivity exceeded 400 µS/cm, placing it outside the claim requirement.
In response, Steros submitted additional experimental evidence during the appeal, attempting to show that an example embodiment in EP 4249647 could also use an overall emulsion with conductivity above 10 µS/cm. The Court was critical, finding that the experiments did not reflect how a skilled person would implement the example consistent with the claimed invention. The Court also noted that experimental data was not disclosed in the patent specification and therefore could not be used to aid in the interpretation of the claims.
Consequently, the appeal was allowed, the preliminary injunction against Otec was lifted, and no likelihood of infringement was established.
A particularly notable element of the decision appears in the headnote, where the Court stated that experimental data not disclosed in the patent specification are generally not relevant to interpreting the claims.
Concluding Remarks
The decision in Otec v. Steros highlights the importance of drafting clear and complete claims and descriptions at the time of filing.
The decision highlights that, at the UPC, experimental data generated after filing is generally not permitted to support a specific interpretation of the claims.
While the decision indicates that post-filing experimental may be relied upon in claim interpretation in some undefined exceptional circumstances, such cases are likely to be limited. This ruling serves as an important reminder for practitioners to ensure that the scope and meaning of claims are clearly established from the outset, removing the need to rely on experimental data not included in the patent specification when construing the claims.
