UPF
Also called Ultraviolet Protection Factor, UPF 50+
Ultraviolet Protection Factor, the rating for fabric. UPF 50+ means the material passes less than one fiftieth of the UV that hits it.
UPF is to cloth what SPF is to lotion. A UPF 30 fabric lets through about one thirtieth of the ultraviolet radiation striking it; UPF 50+ lets through less than one fiftieth, which is the top of the scale and the number worth looking for.
It comes from weave density, fibre type, color and any treatment applied. Tightly woven synthetics rate highest, dark colors rate higher than light ones of the same weave, and stretched or wet fabric rates lower than it does dry and relaxed. That last point is why sizing a sun shirt down protects you less: stretched fabric opens the weave.
An ordinary white cotton t-shirt is roughly UPF 5, and less than that when wet. That is the comparison that makes a rated long sleeve worth the money.
Buy the shirt in your normal size or a size up. A tight UPF shirt stretches its weave open and rates lower than the label says.
Common questions
What does UPF 50+ mean?
The fabric lets through less than one fiftieth, or two percent, of the ultraviolet radiation that reaches it. It is the highest rating on the scale and the standard for fishing sun shirts.
Is a long sleeve shirt cooler than short sleeves in the sun?
In direct sun, usually yes. A light synthetic long sleeve blocks the radiant heat of the sun and moves sweat off your skin, while bare arms absorb everything.
Related terms
Where this comes up
The guides that use upf and show it on real gear.
UPF is one of 206 terms in the glossary.
Browse the full fishing glossary