When the mercury drops but the mountains are still calling, we're dressing as warm as we can without sacrificing breathability and lightness for our adventures in the most frigid of conditions. Under Armour's Packaged Base 4. 0 1/4-Zip Top wicks sweat and dry quickly so we can plan for steep hikes without the risk of overheating. Stretch construction allows total mobility, and a quarter-length front zipper makes it easy to adjust when we warm up. Anti-odor treatment keeps us fresh after multiple days, and a brushed grid fabric traps air against our skin for maximum warmth.