What is a product-by-process claim?
A product-by-process claim is a patent claim that defines a product by the process used to make it, rather than solely by the product's own structure or composition.
When product-by-process claims are used
Product-by-process claiming is appropriate where the product can only be defined by the process steps by which it is made, or where those manufacturing steps would be expected to impart distinctive structural characteristics to the final product.
A representative example: a novel polymer formed by a proprietary crosslinking technique, where the three-dimensional bonding architecture cannot be captured by conventional structural formulas, but where the crosslinking process reliably produces a product with a distinctive and reproducible structure.
A product-by-process claim for such a product might read: "A polymer comprising crosslinked polyacrylic acid chains, wherein the polymer is prepared by reacting polyacrylic acid with compound X at 80 degrees Celsius for 24 hours."
The patentability standard: the product controls, not the process
The fundamental rule is that patentability depends on the product itself, not the method of production. As established in In re Thorpe, 777 F.2d 695 (Fed. Cir. 1985), if the product in a product-by-process claim is the same as or obvious from a prior art product, the claim is unpatentable, even though the prior art product was made by a completely different process.
In other words, the novelty of the process does not rescue a structurally old product.
Process terms as structural limitations
The MPEP does not treat process terms in a product-by-process claim as purely procedural. The USPTO considers the structure implied by the process steps when assessing patentability; terms such as "welded," "injected molded," or "interbonded" can convey structural limitations rather than mere procedural descriptions. This matters in practice: if the recited process reliably produces a distinctive physical arrangement that is absent from the prior art product, the applicant can argue that structural difference as part of the patentability case.
Examination: the burden-shifting standard
Examiners cannot manufacture products by every possible process to compare them directly. The USPTO therefore uses a burden-shifting approach. Once an examiner establishes that a prior art product appears substantially identical to the claimed product (even if that prior art product was made by a different process), the burden shifts to the applicant to come forward with evidence establishing a nonobvious difference.
An examiner may reject a product-by-process claim under 35 U.S.C. § 102 (anticipation) or § 103 (obviousness), or both alternatively, when a prior art product appears substantially identical to the claimed product.
The practical implication for prosecution: comparative test data prepared before examination begins, showing that the applicant's product has measurably different properties (spectral data, mechanical measurements, biological activity), is the most effective way to meet the shifted burden.
The infringement asymmetry: the sharpest practitioner trap
Product-by-process claims create a well-known asymmetry between patentability and infringement that has direct consequences for enforcement strategy.
For patentability, a prior art product made by a different process can anticipate (and therefore invalidate) a product-by-process claim, because patentability turns on the product, not the process.
For infringement, a product-by-process claim is only infringed by a product made by the process recited in the claim; an accused product made by a different process does not infringe, even if the resulting product is structurally identical.
The Federal Circuit confirmed the validity side of this asymmetry in Amgen Inc. v. F. Hoffmann-La Roche Ltd., 580 F.3d 1340 (Fed. Cir. 2009): a patent is invalid if a product made by the recited process is anticipated by prior art products made by different processes.
The result: a product-by-process claim can be both vulnerable (attacked by prior art products made any way) and narrow (enforceable only against products made by the specific recited process).
Patentability vs. infringement: the asymmetry at a glance
| Scenario | Result |
|---|---|
| Prior art has the same product (made by a different process) | Product-by-process claim is anticipated (invalid) |
| Prior art has an obvious product (made differently) | Product-by-process claim is obvious (invalid) |
| Accused infringer makes the same product by a different process | No infringement |
| Accused infringer uses the exact recited process | Infringement |
Practical notes
- Pair with a straight product claim when possible. If the specification supports a structural description of the product, file both a product-by-process claim and a pure product claim. The product claim covers the product regardless of how it is made, providing the broader enforcement reach that a product-by-process claim alone cannot.
- Annotate the specification with structural properties. Even when filing a product-by-process claim, describe the physical or chemical properties that result from the process. This provides support for amending to a structural claim if prosecution requires it, and helps distinguish prior art by tying process terms to concrete structural implications.
- Prepare comparative data before examination begins. Because the burden shifts to the applicant once the examiner identifies a substantially similar prior art product, having measured property comparisons (spectral analysis, mechanical testing, bioassay results) ready before examination can make the difference between allowance and rejection.
- Audit enforcement strategy before filing. If the primary competitive threat is a rival making the same product by a different process, a product-by-process claim will not stop them. In that case, either pursue a structural product claim or a broader process claim covering multiple routes, rather than relying on a product-by-process claim alone.