Features of the Smartwool Men's Intraknit Merino 250 Thermal 1/4 Zip Engineered construction Uses knit structures to enhance Performance with a sophisticated finish Insulating terry loops Are seamlessly paired mesh ventilation in gender-specific zones designed to balance warmth and breathability 3D mapping results in near custom Fit and freedom of movement while ribbed elbows provide added durability Knit-in reflective elements enhance visibility in low light conditions 100% Merino yarn provides the full power of merino with unparalleled management, Insulation, thermoregulation, and odor control Fabric Details 100% Merino Wool