The stack height refers to the amount of material between your foot and the ground in a running shoe. For Under Armour's HOVR line, the stack height can vary depending on the specific model. For example, the UA HOVR Mega 2 Clone has a stack height of 32mm. This means 32mm of cushioning and material between your foot and the ground when you wear these shoes. The HOVR Summit Fat Tire Cuff is even taller, with a stack height of 37mm in the heel and 31mm in the forefoot.