Many believe it is the most important part of any running shoe. It controls excessive foot motion and
provides cushioning, and
shock absorption. Some synthetic foams are used for the midsole, they are light, but not durable. Polyurethane is also commonly used, although durable, it is denser, heavier, and harder. Many shoes are now cushioned with gel, airbags, silicone, or foam capsules. These are all attempts to increase cushioning and durability at the same time.