## Facts

- Festo owned two patents (the Stoll and Carroll patents) covering magnetically coupled rodless cylinders.
- During prosecution of the Stoll patent, the USPTO rejected claims for inadequate description under 35 U.S.C. § 112; Festo amended the claims to require (1) a piston with a pair of one-way sealing rings and (2) an outer sleeve made of magnetizable material.
- During reexamination of the Carroll patent, Festo amended claims (including adding a sealing-ring limitation) to distinguish prior art.
- SMC sold competing rodless cylinders that used (1) a single two-way sealing ring instead of a pair of one-way rings and (2) a non-magnetizable sleeve (such as aluminum) instead of a magnetizable sleeve.
- The parties agreed there was no literal infringement; the dispute was whether SMC infringed under the doctrine of equivalents and whether prosecution history estoppel barred equivalents due to the narrowing amendments.
- After extensive prior proceedings applying the Supreme Court’s rebuttable-presumption approach to estoppel, the district court on remand largely held Festo did not rebut estoppel and entered judgment for SMC; Festo appealed.

## Issues

1. Whether Festo rebutted the presumption of prosecution history estoppel for the amended limitations as applied to (a) a single two-way sealing ring and (b) a non-magnetizable sleeve.
2. If estoppel was rebutted for any limitation, whether the evidence supported infringement under the doctrine of equivalents.
3. Whether the district court correctly applied the governing remand framework, including foreseeability, tangential relation, and other-reason rebuttal categories on a limitation-by-limitation basis.

## Decision

- The Federal Circuit affirmed in substantial part that Festo’s narrowing, patentability-related amendments triggered a presumption of prosecution history estoppel for the amended elements.
- The court affirmed that estoppel barred equivalents for limitations where Festo failed to carry its burden to rebut surrender under the established rebuttal categories.
- The court reversed in part where the district court applied an unduly restrictive view of the rebuttal framework, holding that Festo made a sufficient showing as to certain alleged equivalents to avoid an absolute bar at that stage.
- The result limited the availability of the doctrine of equivalents for the accused products, with some alleged equivalents barred by estoppel and others remaining potentially available depending on the evidentiary record.

## Legal Principles

- A narrowing claim amendment made for reasons related to patentability presumptively surrenders all equivalents between the original and amended claim scope for the amended element.
- The patentee bears the burden to rebut the presumption by showing: (1) the equivalent was unforeseeable at the time of amendment, (2) the amendment’s rationale was only tangentially related to the equivalent, or (3) another reason indicates the patentee could not reasonably have claimed the substitute.
- Estoppel and rebuttal must be evaluated on a limitation-by-limitation basis for the specific amended element and the specific equivalent asserted.
- Foreseeability is assessed objectively at the time of amendment from the standpoint of a person of ordinary skill in the art; known alternatives weigh against rebuttal.
- The tangential-relation inquiry turns on the reason for the amendment; when the amendment addressed the very aspect in which the accused product differs, rebuttal is difficult.
- While underlying technological and historical facts may be reviewed deferentially, the application of those facts to the rebuttal categories is a legal or mixed determination subject to closer appellate scrutiny.

## Conclusion

The Federal Circuit applied the Supreme Court’s rebuttable-presumption approach to prosecution history estoppel, holding that Festo’s narrowing amendments presumptively surrendered equivalents for the amended limitations and that only a fact-supported showing of unforeseeability, tangential relation, or a comparable justification could preserve doctrine-of-equivalents coverage for particular substitutes.


Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 493 F.3d 1368 (Fed. Cir. 2007)