Sweat activated what? Yes, the Zero Rules polo has sweat-activated, super-cooling technology, and that’s not all. It also wicks and has UPF 30 protection from the sun, and features comfort stretch fabric. Technically, it’s a great shirt. Features: Omni-Freeze ZERO™ sweat-activated super cooling Omni-Wick™ Omni-Shade™ UPF 30 sun protection Antimicrobial treatment protects this product from bacterial growth Comfort stretch Active Fit Center back length: 27" FABRIC: Omni-Freeze ZERO™ Interlock 100% polyester Omni-Freeze™ ZERO:Sweat-Activated Cooling OMNI-WICK®:High-Performance Wicking Fabric OMNI-SHADE®: Sun Protection