What is “Materially Identical?”

The doctrine of issue preclusion can prevent an issue previously litigated at the PTAB from being re-litigated in a later proceeding, such as in the district court. In order for issue preclusion to apply, a “materially identical” issue must have been “actually litigated and determined by a valid and final judgment,” where the determination was “essential to the judgment.” See Papst Licensing GMBH & Co. KG v. Samsung Elecs. Am., Inc., 924 F.3d 1243, 1252 (Fed. Cir. 2019). Thus, once appeals have been exhausted, the determinations in a FWD from the PTAB may have preclusive effect in future actions, even on related patents so long as they raise “materially identical” issues.

Which begs the question: What is the scope of materially identical?
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