All-over mesh material for superior ventilation.No side or back seams for ultimate comfort.4-way stretch construction moves better in every direction.Material wicks sweat & dries really fast.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..