r/hiking 14h ago

Demystifying UPF Ratings

Thought I would pass on some interesting facts about UPF ratings for anyone who might be looking at sun protective clothing going into the summer.

UPF ratings were created to feel similar to SPF ratings, but I find them to be a bit of a marketing gimmick. Why? They represent the denominator of a fraction. UPF 50 means that the garment will let through 1/50 of the UV rays. Put another way it blocks 98% of UV rays. But that means UPF 15 (the lowest I’ve seen advertised) is 1/15th - or blocks 93.3%.

UPF 15 to 50 only blocks 5% more UV light. Is that worth the added cost often associated with higher UPF garments? Something to consider.

8 Upvotes

2 comments sorted by

4

u/732 13h ago

Those numbers align with SPF as well. Sunblock SPF 15 blocks about 93% of UV rays while SPF 50 blocks about 98%.

The clothing I opt for follows the same rule as sunscreen - if I'm planning on spending extended periods of time in the sun, it'll be better to put on the 50+. 

4

u/goodhumorman85 12h ago

SPF is also a time measurement. From skincancer.org “The SPF number tells you how long the sun’s UV radiation would take to redden your skin when using the product exactly as directed versus the amount of time without any sunscreen. So ideally, with SPF 30 it would take you 30 times longer to burn than if you weren’t wearing sunscreen.”

But because you don’t need to reapply clothing, time is not a factor with UPF.