UA Base™ 4.0 is built for extreme cold weather and lower activity. Their unique pattern traps heat without adding bulk. Think long underwear, revamped for today''s top athletes.. UA Base™ 4.0 Extreme Baselayer is our warmest yet, delivering extreme warmth in the extreme cold. 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. Inseam: YMD 24.5'''' (+/- 1.5'''' per size). 81% Polyester/19% Elastarell.