Engineered for Performance, our High Performance socks hug your feet, prevent blisters and keep feet dry and comfortable all day long. Ultra Light socks are super thin and extra breathable, and are designed to keep feet cool under the most intense conditions. These socks take up less room in the shoe and are perfect for those who prefer a lighter, cooler feel. The anatomical design enhances fit, delivering maximum comfort and protection by eliminating blisters. Sizing Instructions - Our socks are unisex and fit according to shoe size. If you size up your running shoes, we recommend that you go by your casual shoe size. (See images for size chart). Although the Lycra in our products contracts when it is exposed to water and heat in the wash, it has incredible recovery properties so Feetures socks will stretch back to their original size after the wash. Washing Instructions - Machine wash cold. Hang to dry. No bleach or fabric softeners. For best results, wash socks inside out.