It is long enough for an entire phase of a life to unfold.

Mary Kenner spent eighteen years with a patent on an invention she knew was commercially viable and practically useful, unable to bring it to market because of racial discrimination.

In 1957 — the year after her patent was granted — Procter and Gamble introduced the first mass-market adhesive sanitary pad, which was based on a different approach to the adhesion problem than Kenner’s belt-and-holder design.

The disposable pad approach eventually supplanted the belt-and-holder approach entirely, and today’s menstrual product market is dominated by adhesive products that are quite different from what Kenner patented.