How UPF 50+ actually works

A UPF 50+ rating means the fabric lets through less than one fiftieth of the ultraviolet radiation that hits it. In plain terms, over 98% of the UVA and UVB reaching the cloth is stopped before it touches your skin.

The number comes from the weave, not from a coating. Tightly knit yarn leaves fewer gaps for light to pass through, and technical fibres are engineered to absorb and scatter UV. Because the protection is built into the thread, it does not rub off, sweat off, or wash out. A plain cotton t-shirt sits around UPF 5 to 7, and drops lower once it is wet.

That is the whole reason a UV shirt beats a regular one on a long day outside. You put it on in the morning and it protects for as long as you keep it on, with nothing to reapply.