Under Armour Heatgear Sonic 3" Shorts - Girls' Grade School The Under Armour HeatGear Sonic Short for girls features the signature moisture transport system that wicks sweat away quickly, leaving your skin cool and dry. The fabric is lightweight and designed with a four-way stretch for added mobility. HeatGearŪ works best in weather between 75 and 100 degrees. 3" inseam. 84% polyester/16% spandex. Imported.