The Under Armour Men's Base 2.0 Leggings is constructed using a special negative grid pattern with each individual cell designed to trap heat without adding bulk. Think long underwear, reengineered for athletes performing at their peak. UA Base 2.0 is built for cold weather and higher activity levels. The UA Base is a system of baselayers, numbered from 2.0 to 4.0, that takes you from cold to absolutely freezing temps.