midsole

The midsole is the layer of a shoe situated between the insole (footbed) and the outsole. It primarily provides cushioning to reduce impact forces and contributes to the shoe’s overall stability, support, and energy return during movement. In some designs, it also influences the feel of the ride and the transition from heel strike to toe-off.

Midsole construction relies on foam materials, with ethylene-vinyl acetate (EVA) and polyurethane (PU) being common choices. EVA foams are lightweight and offer good shock absorption, while PU foams tend to be denser and more durable. Some midsoles incorporate additional components such as gel, air units, or hard plates to adjust cushioning, responsiveness, or stiffness. Modern midsoles may use dual-density foams to provide different levels of support in the heel and forefoot, and may embed energy-return systems or carbon fiber plates to enhance propulsion.

Design aspects influence performance and fit. Stack height, the vertical thickness of the midsole, affects cushioning and stability and is a key attribute in performance-focused footwear. The midsole can be tuned for stability, plush cushioning, or a balance of responsiveness and support. Some shoes use rocker geometry or beveled edges to aid smooth transitions during gait.

Durability and care considerations are also relevant. Foam cushioning gradually compresses with use, reducing shock absorption over time. Fatigue or damage to the midsole can alter ride quality and ankle stability. Cleaning should follow manufacturer guidelines, and replacement is generally advised when cushioning or stability deteriorates noticeably, or the outsole has worn through.