From the manufacturer

Men's HeatGear Armour Mock Sleeveless

HeatGear Armour is our original performance baselayer—the one you put on first and take off last. So we made it extra comfortable by wicking sweat and stretching so you can move no matter what.

• Compression: Ultra-tight, second-skin fit.
• Super-light HeatGear fabric delivers superior coverage without weighing you down
• Mesh underarm & back panels for strategic ventilation
• Material wicks sweat & dries really fast
• Ergonomic design keeps seams off high abrasion areas & increases durability