The part of the running shoe between the upper and outsole that provides cushioning and support. Most midsoles are made of either EVA (ethylene vinyl acetate) or polyurethane foam. EVA is lighter and more flexible than polyurethane, but it is not as durable. It can come in various densities with gray-colored EVA being denser than white. The denser, grey EVA is usually placed along the medial side of the shoe to provide stability and motion control and is often referred to as a "medial post." Some midsoles have additional cushioning technology such as air, gel, grids, etc.