Under Armour Boys' HeatGear Armour Up Fadeaway Fitted Long Sleeve Shirt 90% Polyester, 10% Elastane Imported Fitted: Next-to-skin without the squeeze HeatGear fabric is ultra-soft & smooth for extreme comfort with very little weight Stretch-mesh underarm panels deliver strategic ventilation 4-way stretch fabrication allows greater mobility in any direction Moisture Transport System wicks sweat & dries fast