You sweat to keep cool, and that's the idea behind this Columbia® PFG Zero RulesTM Shirt. Omni-FREEZE ZERO's next-to-skin comfort is aided by blue rings that cool you down as you sweat. They also accelerate the wicking process. The Shirt even has Omni-SHADE UPF 30 to help keep sun rays from harming your skin. For the hottest and most humid of days, especially fishing, play with ZERO Rules.