Thirty 48 - Ru Running Series Socks The Ru Running Series is about innovation, with extra padding on the metatarsal provides abrasion protection from your shoes lacing, you will not get any more bruises after a long run. There is also a thin micromesh fabric to allow your feet to breathe. Elastic Arch Support - This minimize Friction And Supports The Plantar Arch Of Your Foot Extra Padding On The Metatarsal Provides Abrasion Protection From Your Shoes Lacing The Rear Heel Tab Helps With Slipping Your Socks On and Off CatalystAF - A Patent-Pending Design Which Creates Airflow In The Fabric To Induce Airflow COOLMAX Fabric Is Designed To Move Moisture Away From The Body Keeping You Feeling Cool And Dry Highlights: What's Right is Right - Each foot has its own curves and features. Check the inner cuff for the right sock for the right foot, or left. Padded Instep - Extra padding on the metatarsal provides abrasion protection from your shoes lacing. How big is it? - The back inside cuff denotes size with simple squares. Note chart by heel of the foot below. Curled Tab - The rear heel tab helps with slipping your socks on and off. CatalystAF - A patent-pending design which creates airflow in the fabric by creating channles to induce airflow. Feel the Heel - For the Ru Series we added more cushion for comfort as you run. Elastic Arch Support - This minimize friction and supports the plantar arch of your foot. Like a Convertible - This thin micromesh fabric allows your feet to breathe. COOLMAX fabric is designed to move moisture away from the body keeping you feeling cool and dry. Materials: 33% CoolMax, 27% Cotton, 30% Nylon, 8% Polyester, 2% Lycra