Under Armour Men's ColdGear Base 4.0 Half Zip Long Sleeve Shirt - UA Base is a system of baselayers, numbered from 2.0 – 4.0, that takes you from cold to absolutely freezing temps. It uses a special negative grid structure to trap heat without adding bulk. Think long underwear, reengineered for athletes performing at their peak. UA Base 4.0 is built for extreme cold weather and lower activity levels. Fitted: Next-to-skin without the squeeze. 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 ¼ zip front allows you to dump excess heat quickly & efficiently 81% Polyester/19% Elasterell Imported Style: 1343242