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" Uses: Hiking FABRIC: Omni-Freeze ZERO® Interlock 100% polyester Omni-Freeze® ZERO Sweat-Activated Cooling OMNI-WICK® High-Performance Wicking Fabric OMNI-SHADE®  Sun Protection