KewlShirt Cooling Tank Top - Step up your Training! - BLACK-SM Traditional Tank Top styling, made with Spandex, HyperKewlTM fabric and waterproof nylon Designed to be worn against the skin for maximum cooling effect, with ventilation vents built into back and front panels Best worn underneath a breathable sports jersey or on its own Can provide 5-10 hours of cooling relief per soaking Can provide 5-10 hours of cooling relief per soaking. Lightweight, easy to activate, and durable Comfortable spandex and nylon outer with HyperKewl fabric inner, water repellent nylon liner