The Casio F-91W is the most famous cheap watch ever made. Billions of wrists, zero changes in decades, and a design so settled that Casio barely touches it. So when Casio does touch it, it is worth paying attention.
The F-91WB is the bio-resin version: the same legendary digital, now with a band made from bio-based resin and a cleaner, more minimalist dial. Watch the unboxing above for the quick look, then read on for what bio-resin actually means, what is different, and whether it is worth the small premium.
What “bio-resin” actually means
Bio-based resin is resin produced using renewable organic resources instead of relying entirely on petroleum feedstocks. Casio’s own wording is careful here: the material is “expected to help reduce environmental impact.” It is a step toward lower-carbon manufacturing, and it is part of a wider Casio push that now covers G-Shock models and the step-tracking F-B100W as well.
What it is not: biodegradable. This is not a compostable watch band. It will not break down in a landfill any faster than regular resin. Bio-based means the carbon in the plastic started life as a plant rather than crude oil. That is a real difference in how it is made, not a magic eco material.
In practice, the band looks and feels like the standard F-91W strap. Same flexibility, same buckle, same 145 to 200 mm fit range. You would not know it was bio-based unless someone told you, which is arguably the point: no compromise in daily use.
What is different from the standard F-91W
Under the hood, nothing. The F-91WB runs the same module 593 as the classic: the same 1/100-second stopwatch, daily alarm, hourly time signal, green LED backlight, auto-calendar, and the famous CR2016 battery rated for approximately 7 years. Same 38.2 x 35.2 x 8.5 mm resin case, same featherweight 21 grams, same splash-level water resistance (fine for rain and hand washing, not for swimming).
Two things actually changed:
1. The bio-based resin band. Covered above. Same feel, greener feedstock.
2. The minimalist dial. This is the visible difference. The F-91WB face drops some of the mode indicators and text clutter of the original, giving it a cleaner, more modern look. Casio’s product copy calls it a “minimalist face, fewer mode indicators,” and side by side with the classic, the WB looks noticeably tidier. If you always found the original F-91W dial a bit busy, this is the version for you.
The WB also comes in colourways the classic never had. Casio lists the F-91WB-1A in black, F-91WB-7A in white, F-91WB-2A1 in blue, and F-91WB-8A in grey, and there is even a Tiffany blue version floating around. The classic F-91W is black, full stop (unless you count the gold-tone F-91WG). If you want an F-91 in white or blue, the WB is the only factory option.
Do not confuse it with the F-91WF
Casio now has two eco-minded F-91 variants and the model numbers are one letter apart, so let us be clear. The F-91WB (this watch) keeps the resin strap but switches it to bio-based resin, and cleans up the dial. The F-91WF is the 2026 update that replaces the resin strap entirely with a woven fabric strap made from recycled PET fibres, aimed at hikers and outdoor wear. The WF launched in Japan in August 2026 and reached the US at $45.95, roughly double the street price of a standard F-91W. Different strap philosophy, different price bracket, different watch. We covered the F-91WF separately.
The specs, verified
Model: Casio F-91WB-1A (black; also -7A white, -2A1 blue, -8A grey). Module: 593 (same as the classic F-91W). Case: 38.2 x 35.2 x 8.5 mm resin, 21 g. Band: bio-based resin, fits 145 to 200 mm wrists. Water resistance: water resistant (splashes and rain, not swimming). Battery: CR2016, approximately 7 years. Light: green LED backlight. Functions: 1/100-second stopwatch, daily alarm, hourly time signal, auto-calendar, 12/24-hour format. Accuracy: plus or minus 30 seconds per month.
Is it worth the premium?
The standard F-91W-1 sells on the street for around $19 to $22 USD. The F-91WB typically lands around $30, so you are paying roughly ten dollars more. What does that buy you? A band made from renewable feedstocks, a cleaner dial, and access to the white, blue, and grey colourways.
That is an honest trade. You are not getting better specs or longer battery life. You are getting the same watch with a tidier face and a slightly greener conscience. If the minimalist dial or a non-black colourway appeals to you, the premium is small enough to be a non-issue. If you just want the cheapest possible F-91W, the classic is still sitting there at twenty bucks, and nobody will blame you.
Watch out for fakes
If the price looks too good, the module feels wrong, or the printing looks off, check our guide on how to spot a fake Casio F-91W before you buy. The same three checks apply to the bio-resin models.
Price and where to buy
The F-91WB-1A in black is the safe pick and usually the easiest to find. Expect to pay around $30 USD, a few dollars more than the standard F-91W.
Check the current price on Amazon: Casio F-91WB-1A (Bio-Based Resin) on Amazon (affiliate link, supports the channel at no extra cost to you)
Verdict
The F-91WB is Casio doing the minimum, in the best way. Same legendary module, same 7-year battery, same twenty-one grams of nothing on your wrist, now with a bio-based resin band and a dial that finally tidies up the clutter. It is the F-91W, slightly greener and slightly better looking, for about ten dollars more than the classic. That is an easy yes if you were buying an F-91W anyway.
Specs verified against Casio’s official product page and dealer listings, October 2026. The F-91WF fabric-strap model is a separate release. Prices move around, so check the live Amazon price before buying.