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 Wide, flat waistband with a rise that sits just right on your hips 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.