Zoot Sports Men's Ultra Run Icefil Singlet 79% Nylon/21% Spandex Imported Icefil combines Xylitol and thermal radiation nano technology, reducing skin temperature up to 5.4F/3C; Waistband and Pocket Overlay: 228g Icefil mesh back for enhanced ventilation and cooling Flatlock stitch construction ensures next-to-skin comfort and minimizes chafing