We gave the base layer an upgrade with performance fabric and a slimmer fit. Our VentTEK™ Underscrub features built-in breathability for extra warmth without overheating. VentTEK Underscrub Baselayer Product Features : Silver-based FreshTEK+™ sustainable odor resistanceVentTEK™ technology enables airflowClimateTEK™ for dynamic and temperature regulated coolingStain repellentMoisture Movement Technology™ wicks away moisture from skinGreater Arm Mobility™ for freedom of movementDuraStretch™ fabric for durable flex, Breathable mesh insets at sides, back and under arms, Convenient locker loop, This product contains materials that meet the bluesign® sustainability standards Men's VentTEK Underscrub Baselayer in Black, Size: Medium by Ariat