Under Armour® BaseTM 4.0 Leggings. Reliable warmth for the most extreme conditions! Your first -- and best -- layer of defense against extreme cold! Under Armour Base 4.0 Leggings are Under Armour's thickest, warmest base layer, making them ideal for cold weather hunting, sports and chores. Equipped with ArmourBlock anti-odor technology to help prevent and eliminate tell-tale odors.