An EVA midsole is the middle section of a running shoe made from foam known as ethyl vinyl acetate, or EVA for short. The midsole is the part of a running shoe located between the upper and the outsole.
Using a closed cell foam such as EVA creates a cushioning effect as well as stability; the most important factors in a good midsole. Achieving better results than the alternative, polyurethane, EVA is the most popular choice when making a midsole for a running shoe. EVA midsoles are also often embedded with secondary cushioning systems such as encapsulated air or gel.