The Under Armour Women's ColdGear Authentic Base Leggings are a top-rated choice for women's synthetic base layer bottoms on Amazon. These leggings are designed to provide warmth and comfort during cold weather activities. They are made with a blend of polyester and elastane, which offers a soft and stretchy fit. The ColdGear technology helps to retain body heat and keep you warm without adding bulk. These leggings also feature a moisture-wicking fabric that helps to keep you dry and comfortable during intense workouts. With a wide waistband and a fitted silhouette, these leggings offer a flattering and supportive fit. They are available in various sizes and colors to suit different preferences.