Zoot Sports Men's Ultra Recovery 2.0 CRX Socks 85% Nylon/15% spandex Imported Achilles tendon support protects and prevents irritable tendons Places direct pressure on the muscles to prevent post-exercise swelling by forcing lactic acid out of the muscles, thus speeding post-workout recovery . CRx = improved blood circulation Anatomically correct left and right foot construction allows targeted pressure to speed post-workout recovery 18-30mmHg compression level