Under Armour Youth Boys HeatGear Performance Crew Socks 2 PACK FABRIC: 90% polyester / 8% nylon / 2% spandex. A Charged Cotton footbed allows for traction control, while the Embedded Arch Support helps reduce foot fatigue. Moisture Transport System that wicks away sweat. ArmourBlock technology that prevents the growth of odor-causing bacteria. YXS/US7, YS/US8 , YMD/US10-12 , YLG/US14-16 , YXL/US18-20.