UA Base 4.0 is built for extreme cold weather and lower activity. It uses a unique pattern that's designed to trap heat without adding bulk. Think long underwear, revamped for today's top athletes. UA Scent Control Technology to keep you undetected in all pursuits. Soft, brushed grid interior traps air, managing your body's microclimate to keep you warm & comfortable. Material wicks sweat & dries really fast. 4-way stretch material moves better in every direction. 1/4 zip front allows you to dump excess heat quickly & efficiently.