Under Armour Women's UA Base 4.0 Crew UA Base 4.0: Mega-grid thermal fleece for the ultimate warmth in the brutal cold Thermal grid fabric traps heat in tiny pockets for long-lasting protection Quick-dry construction wicks moisture to keep you drier, lighter, and more comfortable Lightweight, 4-way stretch construction improves mobility and maintains shape Anti-microbial technology fights odors to keep your gear fresher, longer