Key takeaways
- UPF rates how much UV radiation a fabric blocks — UPF 50 lets through about 1/50th of UV.
- It measures clothing (against UVA and UVB), whereas SPF rates sunscreen on skin (mainly UVB).
- UPF 30–49 is very good and UPF 50+ is excellent protection.
- Sun-protective clothing doesn't wash off or need reapplying, making it a dependable barrier.
Ultraviolet Protection Factor.
What UPF measures
UPF — Ultraviolet Protection Factor — rates how effectively a fabric blocks the sun’s ultraviolet radiation from reaching your skin. A UPF 50 garment lets through only about 1/50th of UV rays (roughly 98% blocked). The higher the number, the more UV the fabric stops.
UPF vs SPF
They’re easy to confuse: UPF rates fabric and accounts for both UVA and UVB, while SPF rates sunscreen on skin and mainly measures UVB. The big practical advantage of UPF clothing is that it doesn’t sweat off, rub off, or need reapplying — it’s a constant barrier over the skin it covers.
On a high-altitude glacier day, a mountaineer wears a UPF 50+ hooded sun shirt for reliable all-day coverage and saves sunscreen for the exposed face, ears, and hands — instead of trying to keep reapplying lotion to their whole body.
Why it matters outdoors
UV intensity climbs with altitude and reflects off water and snow, so long exposed days demand serious sun protection. UPF 30+ is very good and 50+ is excellent. Sun-protective clothing also helps guard against UV-related issues like snow blindness when paired with eye protection.
The bottom line
UPF tells you how much UV a fabric blocks — a simple, reliable measure for sun-protective clothing that, unlike sunscreen, never needs reapplying. Aim for UPF 30+ (50+ is excellent) for long, exposed days, especially at altitude or around water and snow, and pair it with sunscreen on the skin you can't cover.
Frequently asked questions
What does UPF mean?
UPF stands for Ultraviolet Protection Factor and rates how well a fabric shields your skin from the sun's UV radiation. A UPF 50 fabric blocks about 98% of UV, letting through roughly 1/50th. The higher the UPF, the more UV the garment stops.
What's the difference between UPF and SPF?
UPF rates fabric (clothing) and accounts for both UVA and UVB rays, while SPF rates sunscreen applied to skin and primarily measures UVB protection. UPF clothing is convenient because it doesn't rub off, sweat off, or need reapplying like sunscreen does.
Is UPF clothing worth it?
Yes, especially for long days outdoors at altitude or near water and snow, where UV is intense. A UPF 50+ sun shirt provides constant, reliable protection over covered skin without reapplication, complementing sunscreen on exposed areas. Even ordinary clothing offers some protection, but rated UPF garments guarantee it.
Sources
- Sun safety — CDC
- UV protection & textiles — American Academy of Dermatology