Under Armour HeatGear Flyweight Run Singlet - Men'sThe Under Armour HeatGear Flyweight Running Singlet features an ultra-light and smooth fabric that provides extreme comfort and performance without adding weight. The blown-out mesh back provides superior breathability where you need it most. This singlet also includes anti-odor technology and a reflective logo to boost visibility during low-light runs. HeatGearŪ is best for weather between 75-100 degrees. 100% polyester. Imported.