Federal Court Unwraps Foreign File Wrapper In Canadian Patent Litigation

Historically, file wrappers – the back and forth with the Patent Office in a patent application file – were irrelevant and inadmissible in Canadian patent construction. This allowed the Court to focus when construing a patent on the actual language of the claims in the issued patent, while avoiding "opening the pandora's box of file wrapper estoppel"¹. This bar to file wrapper estoppel in Canadian claim construction distinguished Canada from the United States, where prosecution history estoppel was intended "to hold the inventor to the representations made during the application process... by amending, the inventor is deemed to concede the patent does not extend as far as the original claim"².