## Facts

- Improver Corporation owned (by assignment) a European patent covering an electrically powered depilatory device marketed as the “Epilady.”
- The patented device removed hair by rotating a curved helical spring that gripped hairs between its coils and plucked them out.
- Remington marketed a competing depilatory device, “Smooth and Silky.”
- Instead of a metal helical spring, Remington used an arcuate vulcanized rubber rod with slits; when rotated, the slits opened and closed to grip and pluck hair in a functionally similar way.
- The UK action sought relief for patent infringement; the principal dispute was whether the slitted rubber rod fell within a claim requiring a rod “in the form of a helical spring,” properly construed.
- The patent had been litigated in Germany, where courts found infringement, but the UK court addressed infringement under its own construction analysis.

## Issues

1. Whether Remington’s device infringed a claim requiring a “helical spring” where the accused product substituted a functionally similar slitted rubber rod.
2. How purposive construction (including the Protocol to Article 69 EPC) determines whether a non-literal variant is within a claim.
3. What structured inquiry should be used to assess when a variant outside the primary meaning of claim language nevertheless falls within the claim as properly interpreted.

## Decision

- The Patents Court (Hoffmann J) held that Remington’s “Smooth and Silky” device did not infringe the patent.
- The court applied purposive construction and formulated a three-question test (later called the “Improver questions”) for variants.
- Applying that framework:
  - The substitution had no material effect on how the invention worked.
  - That lack of material effect would have been obvious to the skilled person at the relevant date.
  - Nevertheless, the skilled person would understand the claim language to require strict compliance with the primary meaning of “helical spring.”
- Because strict compliance was intended, the slitted rubber rod fell outside the claim scope.

## Legal Principles

- Patent claims are construed purposively through the eyes of the skilled person, not by purely verbal or literal analysis.
- For a variant outside the primary (literal/acontextual) meaning of claim language, the court should ask:
  - Whether the variant materially affects how the invention works; if yes, it is outside the claim.
  - If not, whether the lack of material effect would have been obvious to the skilled person at the relevant date; if no, it is outside the claim.
  - If yes, whether the skilled person would still understand from the claim language that strict compliance with the primary meaning was intended as essential; if yes, it is outside the claim.
- The first two questions primarily address technical equivalence; the third is a question of claim construction focusing on what the claim language would communicate to the skilled reader.
- Functional similarity alone does not establish infringement where purposive construction indicates the patentee chose language that confines the claim to a specific form (here, a “helical spring” in its ordinary sense).

## Conclusion

The court rejected infringement even though the accused product achieved the same depilatory result in substantially the same way, because purposive construction showed the claim required a “helical spring” in its primary meaning; the decision is best known for the three “Improver questions” used to analyze whether a non-literal variant falls within a patent claim.


Improver Corp. v. Remington Consumer Prods. Ltd., [1990] F.S.R. 181 (Ch. 1989)