Under Armour LowCut Socks (3 Pack) 99% Polyester/1% Spandex Imported Strategic cushion reduces bulk, delivers flexibility and breathability HeatGear fabric wicks sweat away from your skin to keep you cool, dry, and light ArmourBlock Technology helps prevent growth of odor causing bacteria in the sock The chart of the back of the product is the shoe size, not the sock size 6-18 Months is size YXS which is 4-5.5 in the sock industry