100% Micro-PolyesterEC2® Qwik-Dri™:Fast wicking and dryingInhibits the growth of bacteria that causes odorThe dual-ply microfiber fabric traps air and allows breathabilityMidweight warmth (2.0) makes Authentic Thermal extremely versatileUPF rating 25+Flat seam construction for comfortVendor Style Number: W8359 Terramar Men's 2-Layer Authentic Thermal Crew