Threadborne Siro fabric gives greater stretch & recovery, ultra-soft feel & more breathable performance.Material wicks sweat & dries really fast.Flatlock seams eliminate chafing.Where we started? It all started with an idea to build a superior T-shirt.The technology behind Under Armour's diverse product assortment for men, women and youth is complex, but the program for reaping the benefits is simple: wear HeatGear when it's hot, ColdGear when it's cold, and AllSeasonGear between the extremes..