The F-91W has been made continuously since 1989 and is one of the best-selling watches in history. Casio has now changed exactly one component of it, and the change is a good one.
The resin strap was always the weak part. It is fine at a desk and unpleasant on a long walk, where it holds sweat against the wrist. Collectors solved this years ago by buying the $20 watch and putting a $5 nylon strap on it, which is such common practice that it barely counts as a modification. The F-91WF is Casio conceding the point.
What Casio actually says about the new band is more interesting than “fabric”: it is a lightweight woven band made from recycled fibre, and the company claims it is both scratch- and stain-resistant. Regional listings describe it as recycled PET — bottle plastic, shredded and respun — which is a neat thing to do with the strap on a watch whose entire identity is cheapness done well. It comes in three references: F-91WF-1A in black, F-91WF-2A in navy, F-91WF-3A in olive.
Everything else is untouched, and that is the point. Same 35.2mm resin case, same 8.5mm thickness, same 30m water resistance, same stopwatch, daily alarm and auto-calendar, same CR2016 rated for seven years. There is no new module and no new claim. Casio changed the strap and stopped.
Two honest caveats, and the first is the awkward one. This costs roughly double the watch it is based on. Confirmed regional pricing runs around ฿1,600 in Thailand (about $48) and 1,487,000 VND in Vietnam (about $57), against $20–30 for the standard resin F-91W. You are paying something like twenty-five dollars for a strap that the aftermarket sells for five, and if you already own an F-91W the rational move is a NATO strap and a spring bar tool. Second: there is still no announced US or European price or release date. As of writing, the Western launch is unconfirmed, so anything you find in a marketplace listing right now is an import at an import’s markup.
And 30m water resistance means rain and sweat, not swimming. That was always true of the F-91W; it is worth restating on one being sold as trail-ready.
None of which stops it being the right answer to a real question. If you want one watch that weighs nothing, runs for seven years, tells you the time in the dark and can be replaced for the price of lunch if you lose it on a mountain, this is now that watch with a strap that breathes. Wait for the local price.