37.5® is a fabric treatment technology that uses active particles from volcanic sand with billions of micropores, massively increasing the surface area of the material by up to 800%. When you're hot, the active particles use your body's energy to remove moisture and cool you down. This can result in better performance, increased efficiency and greater comfort. Click here for more information.

Some users report that backpack rubbing can cause some pilling on Iced Tee fabric (try Sherpa Shorts for run storage!) However, our personal testing during ultras up to 20hrs found no evidence of this which suggests it may be pack or vest-specific.