Midsoles

The midsole is the part of a shoe located between the outsole and the insole. It is primarily responsible for cushioning, impact absorption, energy return, and stability during movement. The design and materials of the midsole determine how a shoe feels and performs across activities.

Common midsole materials include ethylene-vinyl acetate (EVA) foam, which is lightweight and cushy but can compress over time, and polyurethane (PU), which is denser and more durable. Many modern midsoles use TPU-based foams or proprietary blends that emphasize energy return. Some performance models also incorporate plates made of carbon fiber or other materials to increase stiffness and propulsion without sacrificing cushioning.

Design features such as stack height, heel-to-toe drop, and rocker geometry influence ride quality. Stack height affects cushioning depth and ground clearance, while the drop can alter stride mechanics. A curved or rocker midsole supports smoother rollover, and the stiffness of the midsole structure can affect stability and pronation control.

Midsoles are often categorized by purpose: cushioned, high-stack designs for everyday comfort; stability-focused midsoles that help control inward foot motion; lightweight, responsive foams intended for speed; and high-energy-return formulations aimed at efficiency. Over time, midsole foam can lose resilience as it compresses with use, which can alter cushioning and support. Replacing or rotating footwear as the midsole compresses is common practice for maintaining ride quality.