Midsole
The core of a running shoe, sandwiched between the upper and the outsole, providing cushioning and energy return.
What is the Midsole?
The Midsole is the heart of a running shoe. It sits between the upper (the fabric part) and the outsole (the rubber bottom). It is where the magic happens—cushioning, stability, and energy return.
Key Materials
- EVA (Ethylene Vinyl Acetate): The classic white foam. Reliable, cheap, but can pack out over time.
- PU (Polyurethane): Denser and more durable than EVA, but heavier.
- PEBA (Polyether Block Amide): The "super foam" (e.g., ZoomX, Pwrrun PB). Extremely light and bouncy, used in modern racing shoes.
- TPU (Thermoplastic Polyurethane): Bouncy and durable (e.g., Adidas Boost).
Functions
- Shock Absorption: Compresses on impact to protect your joints.
- Energy Return: Bounces back to propel you forward.
- Stability: Denser foams or plates in the midsole can guide the foot.
You date the upper, but you marry the midsole. — Old shoe dog saying.
Midsole
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Related Terms
Carbon Plate
A stiff carbon fiber plate embedded in racing shoes that provides propulsion and energy return, often called a "legal performance enhancer."
Outsole
The bottom layer of a running shoe that contacts the ground, providing traction and durability.
Stack Height
The total thickness of the shoe sole (midsole + outsole) between your foot and the ground.
Upper
The top part of a running shoe that holds the foot in place, typically made of engineered mesh or knit materials.
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