UV Protection in Functional Underwear for Outdoor Use

If you're into hiking, trail running, or just spending long hours under the sun, you’ve probably asked yourself: does my functional underwear actually protect me from UV rays? Spoiler: not all base layers are created equal. As a long-time outdoor gear reviewer and former outdoor guide, I’ve tested over 30 brands of performance underwear in high-exposure environments—from the Atacama Desert to the Rocky Mountains. Let me break down what really works.

The key metric? UPF (Ultraviolet Protection Factor). Unlike SPF (which is for sunscreen), UPF measures how much UV radiation a fabric blocks. A UPF 50 fabric blocks 98% of UV rays—meaning only 1/50th gets through. That’s the gold standard recommended by the Skin Cancer Foundation.

Here’s a quick comparison of common materials used in functional underwear:

As you can see, functional underwear with UV protection made from tightly woven polyester outperforms others in blocking harmful rays. But here’s what most brands won’t tell you: stretching the fabric or wetting it can reduce UPF by up to 40%. That’s why fit and construction matter as much as material.

I personally swear by brands like Icebreaker and Smartwool for alpine conditions, but for desert hikes, I go with underwear with UPF 50+ from ExOfficio or Patagonia. They use special coatings and denser knits that maintain protection even when soaked in sweat.

Pro tip: Look for garments labeled “UPF 50+” and check if they’re certified by independent labs like ARPANSA or the Australian Radiation Protection Agency—yes, Australia knows a thing or two about harsh sun.

In summary: don’t assume your base layer is protecting you. Check the label, understand the fabric, and prioritize certified UV-blocking performance. Your skin will thank you after years of adventure.