UPF 50+ Explained: What the Number Actually Means

SPF (Sun Protection Factor) measures sunscreen. UPF (Ultraviolet Protection Factor) measures fabric. They test different things in different ways, so a “50” on a sunscreen bottle and a “50” on a shirt tag aren’t directly comparable — but the underlying idea is the same: how much UV radiation gets through before it reaches your skin.

A UPF 50+ rating means the fabric blocks about 98% of UV radiation, letting roughly 1/50th through. For context, an ordinary white cotton t-shirt sits around UPF 5-8 when dry — and drops even lower when it’s wet or stretched thin. That’s the gap UPF-rated fabric is built to close.

The rating isn’t just about the fiber. It comes down to a few things working together:

• Weave tightness — a denser weave leaves fewer gaps for UV to pass through

• Fabric weight — thicker fabric generally blocks more, up to a point

• Color — darker colors typically absorb more UV than lighter ones

• Stretch — the more a fabric stretches, the more it thins out and the more protection it can lose. This is part of why a regular cotton shirt isn’t a reliable substitute for sun-protective fabric, even if it feels similarly lightweight.

UV exposure adds up over years, not just during the one afternoon you forgot sunscreen. If you’re regularly outdoors — on the water, on a trail, in a stand at sunrise — the fabric you’re wearing is doing a meaningful share of the protection work, especially on the parts of your body you’re less likely to reapply sunscreen to consistently (shoulders, back, forearms).

UPF-rated clothing also doesn’t wear off, sweat off, or need reapplication the way sunscreen does. It’s protection that’s already handled the moment you put it on.

Not everything labeled “sun protective” is tested and rated the same way. When you’re evaluating a piece, a few practical things to check:

• Is it labeled with an actual UPF number (not just “sun protection” as a vague claim)?

• Does it stay protective when wet? Some fabrics lose significant UPF when soaked.

• Is the fit true, or does it stretch thin under tension? Overstretched fabric can lose rated protection.

Every piece in our performance lineup — the Canyon Performance Quarter Zip, the Bamboo Performance Sun Hoodie, and the Bamboo Heritage Long Sleeve — is built and rated at UPF 50+, so the protection doesn’t change depending on which one you reach for. The only thing that changes is the fit.

UPF 50+ isn’t a marketing number — it’s a measurable standard for how much UV actually reaches your skin. If you’re spending real time outdoors, it’s worth understanding what you’re wearing, not just wearing it.