UPF
Also called Ultraviolet Protection Factor, UPF 50+
What is UPF?
Ultraviolet Protection Factor, the rating for fabric. UPF 50+ means the material passes less than one fiftieth of the UV that hits it.
UPF at a glance
- UPF 50+
- Under 2% UV passes
- Top of the scale
- UPF 30
- About 3% passes
- White cotton tee
- About UPF 5
- And less when wet
- Rated by
- AATCC TM183 and ASTM D6603
What does the UPF number mean?
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.
The rating is not a marketing invention. AATCC Test Method 183 measures how much UV a fabric transmits, and ASTM D6603 sets what a garment may then claim on its label, which is why a rated shirt and an unrated one are not the same purchase.
What makes a fabric block UV?
It comes from weave density, fibre type, colour and any treatment applied. Tightly woven synthetics rate highest, dark colours 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, and the label was measured on a relaxed sample.
Is a UPF shirt better than a normal one?
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: a full day on open water in a cotton tee is a meaningful UV dose through the shirt, not just on the arms.
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.
What this means when you’re choosing
- A stated UPF number rather than the words sun protection. Unrated garments can and do claim protection they have never been tested for.
- A relaxed fit. The rating assumes unstretched fabric, so a shirt you size down is delivering less than its label.
- Coverage over rating past UPF 50+. There is nothing above it on the scale, so a hood, a collar and long sleeves buy more than a bigger number does.
The common mistake
Assuming any long sleeve is sun protection
A loose white cotton shirt feels like coverage and rates around UPF 5, dropping further once it is damp with sweat or lake water. The protection comes from weave density and fibre, not from the fact that the fabric is between you and the sky. If the garment does not carry a tested UPF number, treat it as shade, not as sunscreen.
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.
Where this is defined
- ASTM D6603-19: Standard Specification for Labeling of UV-Protective Textiles, ASTM International
- AATCC Test Methods (TM183, transmittance or blocking of UV radiation), American Association of Textile Chemists and Colorists
- Sun-Protective Clothing, The Skin Cancer Foundation
Where this comes up
The guides that use upf and show it on real gear.
Last reviewed . UPF is one of 222 terms in the fishing glossary.