Sport-Tek PosiCharge RacerMesh Polo. ST640 100% Polyester Thanks to our ultra-fine flat back RacerMesh, this polo has unparalleled breathability for superior cooling. PosiCharge technology locks in color and keeps logos crisp-making this value-priced essential a fan favorite all season long. 3.8-ounce, 100% polyester flat back mesh with PosiCharge technology Tag-free label Moisture-wicking Flat knit collar