Eight inputs — hours, edge condition, chemistry, climate, glass, brand, storage, flip status — and the math says keep working, flip the rubber to the unused edge, replace immediately, or replace and investigate the channel or chemistry that is wearing it abnormally.
pull the rubber, rotate 180°, slide it back in
Effective wear hours: 19.2 (against a 40-hour design life). The first edge has reached the rounding threshold where the line it draws is starting to soften. The flip — a five-second move with no new parts — resets the rubber to the unused second edge and buys roughly another full cycle of useful life. The second edge will reach replace at approximately 11.3 more hours.
Channel-mounted storage is the trade default but accelerates rubber wear by roughly 10% versus sleeved storage. On your most-used squeegees, removing the rubber at end-of-day and storing it in a sleeve extends the rubber life noticeably.
Single-blade rubbers have two working edges by design. Pull the rubber from the channel, rotate it 180°, and slide it back in. The unused edge is now the working edge; the worn edge sits in the channel pocket out of contact with the glass. A flipped rubber resets the wear clock to roughly zero for another route-cycle of work.
Whatever the verdict, a backup rubber in the toolbox costs $7 and saves an end-of-route apology call. If the rubber fails mid-panel, you can swap in twenty seconds and finish the elevation; without the spare, you finish the elevation badly or you stop.