What Makes A Running Shoe - The Midsole

The midsole has come a long way since the mid 1900s. Early athletic shoes offered little more than leather uppers and rubber soles, with almost no cushioning. The introduction of EVA foam in the 1970s changed everything, creating lightweight, shock-absorbing midsoles that became the standard. By the 1980s and ’90s, brands were layering in air, gel, and stability features to improve comfort and control. Today, midsoles are built with advanced “super foams” and even carbon plates, turning this once-simple layer into the performance engine of modern running shoes.

• EVA (Ethylene Vinyl Acetate) – A lightweight foam used in most running and walking shoes. It’s made up of tiny gas-filled bubbles that compress under pressure, providing soft cushioning and shock absorption.

• PU (Polyurethane) – A denser, more durable material often found in work boots and hiking shoes. PU midsoles offer excellent stability and long-lasting support, though they can feel heavier than EVA and tend to break down more visibly over time.

• TPU (Thermoplastic Polyurethane) – A modern midsole foam created by fusing particles through heat. TPU provides higher energy return and greater durability than EVA, while also performing well in a wide range of temperatures. It’s typically heavier but built for responsiveness and longevity.

A midsole isn’t just a block of foam, it’s carefully engineered to influence how your foot moves through every stride. Key design features include:

• Stack Height – The total thickness of the midsole. Higher stacks mean more cushion, while lower stacks keep you closer to the ground for a more natural feel.

• Heel-to-Toe Drop – The difference in height between the heel and forefoot. A higher drop encourages forward momentum and eases strain on calves, while a lower drop promotes a more natural gait.

• Geometry & Rocker Design – Many midsoles are sculpted with curves or rockers to reduce impact and make transitions smoother. These design details can dramatically change how a shoe feels, even with the same materials.

These construction choices are why two shoes with EVA foam can perform completely differently on your feet.

Ever had running shoes that felt amazing in the store but left you sore after a few miles? That often comes down to this cushioning platform’s design and materials.

A well-engineered core layer offers:

• Impact absorption to reduce stress on knees, hips, and feet

• Support for mechanics like pronation or supination

• Energy return for a more effortless stride

• Stability to keep your gait balanced and controlled

These layers range from plush foams to firm, responsive materials. Choosing the right one depends on your unique foot shape and running style.