Under Armour Boys' UA Base 2.0 Leggings - BlackUA Base 2. 0 is built for cold weather and high activity levels. It uses a unique pattern that's designed to trap heat without adding bulk. Think long underwear, revamped for today's top athletes. UA Base 2. 0 Active Baselayer is lightweight, flexible & breathable for high activity performance in cool conditions Soft, brushed grid interior traps air against your skin, closely managing your body's microclimate to keep you warm & comfortable Material