| What it rates | UV blocked by fabric |
| UPF 50 | Blocks ~98% of UV |
| Vs SPF | SPF = sunscreen/UVB; UPF = fabric/UVA+UVB |
| Depends on | Weave, color, weight, treatments |
UPF (Ultraviolet Protection Factor) rates how effectively a fabric blocks ultraviolet radiation from reaching your skin. A UPF 50 fabric lets through only about 1/50th (2%) of UV, blocking roughly 98%. Unlike SPF, which rates sunscreen against UVB, UPF measures clothing against both UVA and UVB, and depends on the fabric’s weave, color, weight, and treatments.
Wearable sun protection
The clothing side of sun protection (vs sunscreen’s SPF), important at altitude where snow blindness is also a risk.
Frequently asked questions
What does UPF mean?
UPF stands for Ultraviolet Protection Factor, a rating of how much ultraviolet radiation a fabric blocks from reaching your skin. A UPF of 50 means only about one-fiftieth of UV penetrates the fabric, so it blocks roughly 98% of UV. Higher UPF means more sun protection from the garment.
What's the difference between UPF and SPF?
SPF (Sun Protection Factor) rates sunscreens, primarily against UVB rays, while UPF rates fabrics against the full UV spectrum (both UVA and UVB). SPF is about what you put on your skin; UPF is about what you wear. Sun-protective clothing with a high UPF is a reliable, reapplication-free complement to sunscreen.
What gives a fabric a high UPF?
Tighter weaves, darker or more saturated colors, heavier fabrics, certain fibers (like polyester), and UV-absorbing treatments all raise UPF. Stretching or wetting a fabric can lower it. UPF-rated clothing is tested to guarantee its protection, which is handy where reapplying sunscreen is impractical, such as at altitude or on the water.
Sources
- UPF clothing — American Hiking Society
- Sun-protective fabrics — The Mountaineers