Brand New Under Armour Sportstyle Size: YL Boys Short Sleeve Hoodie. Under Armour's mission is to make all athletes better through passion, design and the relentless pursuit of innovation. 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 All Season Gear.