The Boys's Integral Long Sleeve Crew from Mountain Hardwear features a Hybrid Merino Wool and polyester fabric that provides the best of both worlds: ultra-fine Merino Wool fibers provide softness and warmth, and fast-drying polyester fibers are durable and wick away sweat. Its MicroClimate Zoning construction places open mesh areas where you necessity it most for breathability, while an anti-microbial Complete controls odor.