Under Armour HeatGear Flyweight Run Short Sleeve Running T-Shirt 100% Polyester HeatGear Flyweight Fabric - Lightweight and smooth, this functional material blend sits comfortably against the skin whilst delivering peerless technical performance. Ventilated Mesh Panelling - Encourages increased airflow around critical heat zones (rear and underam panels). Moisture Transport System - Wicks excess sweat away from the skin and onto the garment's surface, from which it evaporates. Anti-Odour Technology - Quells the spread of odour carrying microbes. Reflective Components - Preserve the wearer's visibility in diminished light.