Under Armour HeatGear Flyweight Run Short Sleeve T-Shirt Regular: A slimmer athletic cut that delivers better mobility by eliminating the bulk of extra fabric. Ultra-light, smooth fabric provides extreme comfort and performance. Mesh back and underarm panels provide strategic ventilation. Signature Moisture Transport System wicks sweat away from the body . Body: 3.2 oz. Polyester. Mesh: 2.2 oz. Polyester. Imported.