The Federal Circuit further clarified the doctrine of claim differentiation in Anderson Corp. v. Fiber Composites, LLC. Andersen Corp. owns a number of patent relating to composite materials made from a mixture of polymer and wood fiber as well as patents that relate to structural parts made from those composite materials. Fiber Composites manufactures and sells deck railing and spindle products under the trade name Fiberon®. Andersen Corp. brought action against Fiber Composites in the District of Minnesota alleging that the Fiberon® products infringed six of Andersen Corp.'s patents.

While discussing the case, the Federal Circuit took the opportunity to address the doctrine of claim differentiation. Claim differentiation is the doctrine based on the common sense notion that different words or phrases used in separate claims are presumed to indicate that the claims have different meanings and scope. To the extent that the absence of such difference in meaning and scope would make a claim superfluous, the doctrine of claim differentiation states the presumption that the difference between claims is significant.

The presumption of difference can be refuted though by the written description and the prosecution history of a patent. The doctrine of claim differentiation can not broaden claims beyond their correct scope, determined in light of the specification and the prosecution history and any relevant extrinsic evidence. Claims that are written in different words may ultimately cover substantially the same subject matter.

To read the full decision in Anderson Corp. v. Fiber Composites, LLC, click here.