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 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
• Performance elastic waistband