UA Base 4.0 Extreme Baselayer is our warmest yet, delivering extreme warmth in the extreme cold; 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