UA Base™ 4.0 Extreme Baselayer is our warmest yet, locking in your body's heat to deliver extreme warmth in the extreme cold. UA Scent Control Technology to keep you undetected in all pursuits. Soft, brushed grid interior traps air against your skin, closely managing your body's microclimate to keep you warm & comfortable. Material wicks sweat & dries really fast. 4-way stretch construction moves better in every direction.