Base layer warmth and wicking with added 10% stretch for the ultimate in warmth and mobility. The Treeline works as a first or second layer depending on the season. Fit: Performance CB: 20.5" CF: 18.5" Fabric: 90% Polyester, 10% Spandex 75wt UltrastretchClassic crew neckFlat seaming for maximum comfortReflective logo