Last year, our colleague Peter Youle wrote about the pitfalls of parameters in patent claims. Whilst small molecules are typically claimed using structural features and formulae, these are usually unsuitable for defining a polymer. Instead, parameters, such as the weight average molecular weight (Mw), are frequently used to characterise polymers.

The position of the European Patent Office (EPO) on the use of parameters in claims is generally as follows:

  • The method for measuring the parameter (or at least a reference to it) must appear completely in the claim itself. This is not necessary if the method for measuring a parameter belongs to the skilled person's common general knowledge or all the measurement methodologies known in the relevant technical field for determining the parameter yield the same result within the appropriate limit of measurement accuracy.
  • The skilled person needs to be able to verify easily and unambiguously whether they are working inside or outside the scope of the claim.

Further complications arise when "unusual parameters" are used, which the EPO defines as parameters that are not standard in the field, or that measure a property that was previously unmeasured in the field. Lack of clarity objections may arise where it is not clear from the application how the unusual parameter may be converted to the standard parameter, and insufficiency objections may also arise where specialist equipment is required to obtain a parameter.

Where parameters seem unavoidable when defining an invention, for example to distinguish the invention from prior art, it may be useful to characterise a product by the method used to produce it, using a so-called product-by-process claim. Such an approach can be used as an alternative to or in addition to the use of parameters. In this article, and from a primarily European perspective, we consider and comment on product-by-process claims, which have particular usefulness in the context of polymer claiming.

Product-by-process claims: when may they be used?

Product-by-process claims, for example with language of the type Product x obtained/obtainable by process y, are often useful where a product is difficult to characterise by reference to its structure or composition. In fact, a threshold requirement applied by many patent offices, including the EPO and UK Intellectual Property Office (UKIPO), is to accept the use of product-by-process claims only if it is (to quote from the EPO's Examiners' Guidelines (Part F, Chapter IV, §4.12)) "impossible to define the claimed product other than in terms of a process of manufacture".

Similarly, in Japan, it is understood that product-by-process claims are only considered valid where, at the priority date, it is technically impossible or too impractical to directly specify a product's structure or property. In contrast, in the US, product-by-process claims may be used for any product regardless of whether or not the product may be defined by structure or property (see Chapter 2100, Section 2113 of the MPEP).

Claim interpretation: validity and infringement

Since a product-by-process claim has both product and process features, the question arises as to whether it is a claim to the product irrespective of how it is made, or a claim to the product only when the method of manufacture specified in the claim is used.

At the EPO, which is a forum only for validity and thus not for infringement, it is settled law since 1984 (case T 150/82) that a product-by-process claim is to a product per se, regardless of the language – for example obtained or obtainable – used in the claim to associate the claimed product with the process specified.

Fundamental requirements for validity of product-by-process claims were clarified in decision T 205/83 (from 1985), in which a patent owned by Maximum was opposed for lack of inventive step. After rejection of the opposition, it was held on appeal that the product-by-process claim, to a vinyl ester / crotonic acid copolymer obtained by polymerizing at least one vinyl ester and crotonic acid, lacked novelty. The patent was maintained, but with deletion of the product-by-process claim.

It was decided in T 205/83 that the product of a known process is not rendered new merely by virtue of a modification to the process: novelty can be established only if evidence is provided that the process results in other products. Since products of the same type were already known in the prior art and the method of manufacture followed the same principles known in the prior art, the Board held that, in the absence of evidence that modification of the process parameters results in other products (the proprietor's assertion of this was not enough), the method of manufacturing the claimed products was merely a procedural modification of a known method.

So T 205/83 gives rise to the EPO's requirement that the product must be novel.

In the UK, the most relevant case law on product-by-process claims is Hospira UK Limited v Genentech Inc. ( [2014] EWHC 3857 (Pat)). In this, amongst other matters, Hospira opposed claim amendments proposed by Genentech to a patent directed towards lyophilized formulations of its anti-cancer drug Herceptin).

Mr Justice Birss (as he then was) clarified that, to be novel, a product obtained or obtainable by a process has to have some novel attribute conferred on it by the process as compared to the known product. For the purposes of validity, product-by-process claims are thus assessed in the UK – as they are at the EPO – as product per se claims and are novel only if the product does not form part of the state of the art. However, it was clarified for the purposes of infringement that a product not obtained by the recited process, where the claim uses obtained by or synonymous language, does not infringe. Where a product is described as being obtainable by a process, it was held that such a claim is infringed (where a different process is used) if the resultant product has every single characteristic which is the inevitable consequence of the process specified in the claim. If something does not have all those attributes then it is not obtainable by the process.

Accordingly "obtained" and "obtainable" product-by-process claims are both treated equally for the analysis of novelty (since the product itself is assessed, irrespective of the method used to make it), but for the purpose of infringement, a claim with "obtainable" language has potentially greater scope, at least in the UK.

More on EPO requirements and case law

In decision T 768/08 (from 2012), the Board considered in detail the clarity requirements for product-by-process claims, and the principles underlying these, noting that the primary purpose of a product claim is to permit comparison with the prior art. Accepting that product-by-process claims fulfil the need of defining chemical substances such as macromolecules, the Board held that all of the specific process conditions (such as starting materials and reaction or formulation or preparation conditions), needed to necessarily obtain the claimed product, as inevitable process product, whose novelty could then be established by e.g. comparative tests, should be defined. For the claim to be clear, these features should make it possible to establish the novelty of the inevitable product of the process recited over the prior art.

The reasoning and requirements set out in EPO decisions such as T 150/82, T 205/83 and T 768/08 essentially hold true today. For example, in the section of the EPO's Examiners' Guidelines dealing with a product-by-process claims (Part F, Chapter IV, §4.12 (which as an aside appears immediately after the section dealing with unusual parameters), it is noted that the "burden of proof for an allegedly distinguishing "product-by-process" feature lies with the applicant, who has to provide evidence that the modification of the process parameters results in another product, for example by showing that distinct differences exist in the properties of the products". In T 32/17, it was held that the burden rests on the proprietor, not the opponent, after grant.

As the same Board of Appeal, with slightly different make up, put it in both T 967/10 and T1988/12, "the requirement for clarity means that the skilled person should be able to determine, either from the claim alone or, by construction of the claim in the light of the description, or by construction in the light of the skilled person's common general knowledge, which identifiable and unambiguous technical features are imparted to the product by the process by which it is defined". T 2295/19 from 2022, and T 2597/17 from 2020, each relating to polymers, refer back to T 205/83 to note that novelty of product-by-process claims requires proof that modification of the process parameters leads to other products.

In our experience, it seems that the EPO examines product claims characterised with parameters (let alone unusual parameters) and product-by-process claims very carefully. In view of this, it makes sense for applicants to consider very carefully how they might best claim novel products, the novelty of which may be difficult to substantiate. Product claims characterised by parameters can be subject to insufficiency objections, before and after grant as well as objections before grant to the clarity of the parameter concerned (see again our colleague Peter Youle's article). In contrast, product-by-process claims, to the best of our knowledge, have not been attacked for being insufficient (at least with respect to the formulation of the claim as a product-by-process claim per se).

Product-by-process claims thus offer an alternative way to rely upon parameters when distinguishing over prior art, without reciting the parameter concerned in the claim. It will be always be advisable to set out as much detail as possible on the measurement of such parameters, and to explain, if appropriate, how these serve to substantiate novelty. To allow such claims, the EPO is not looking for the applicant to identify "every single characteristic which is the inevitable consequence of the process specified in the claim" (cf the remarks of the judge in Hospira UK Limited v Genentech Inc.). Rather, as is reflected in the Guidelines and case law briefly discussed above, EPO Examining and Opposition Divisions want applicants to provide evidence that the product claimed is novel.

Of course, product-by-process claims may be subject to lack of inventive step attacks, and will likely be subject to rigorous analysis in the event that infringement is asserted.


It may sometimes be more straightforward to protect a complex product via a product-by-process claim, using the product's novel attributes (measureable by parameters) to achieve grant, and to defend a product-by-process claim than to do the same with a corresponding parameter-reciting product claim. Both options should be considered when claiming novel polymers and other complex products.

Although they are often overlooked, product-by-process claims should be commonplace in the world of complex product patents.

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.