HeatGear HeatGear was designed to be worn in warm to hot temperatures under equipment or as a single layer. The company 's first compression T-shirt was the original HeatGear product and remained its signature style in 2012. In sharp contrast to a sweat-soaked cotton T-shirt that could weigh two to three pounds, HeatGear was engineered with a microfiber blend featuring what Under Armour termed a "Moisture Tranport System" that ensured the body will stay cool,dry,and light. HeatGear was offered in a variety of tops and bottoms in a broad array of colors and styles for wear in the gym or outside in warm weather. Compression-fit HeatGear reduced muscle fatigue,was particularly popular for training sessions and competition,and was the company 's top-selling gear line year-round.