What are the cushioning materials used in the midsoles of athletic shoes?

1. Foamed TPU

Foamed TPU is actually expanded thermoplastic polyurethane (ETPU) material. Midsoles made from it are often called "popcorn midsoles" due to their shape and foaming process.

ETPU is used in Adidas' Boost series, which emphasizes a "soft and bouncy" feel. The material offers excellent resilience, extremely low compression set, and a comfortable fit, while the manufacturing process is environmentally friendly and efficient.

Saucony's Freedom ISO 2 utilizes EVERUN technology, a supercritical foam material based on ETPU, which is lightweight, highly responsive, and provides durable cushioning. Unlike Adidas Boost's "soft → springy → loose" feel, EVERUN's feel is described as a progressive feedback of "soft → springy → solid," making it more suitable for maintaining stability during fast running.

The midsole of the Xtep Power Nest X uses ETPSIU elastic material (a modified thermoplastic polyurethane), which is made through supercritical fluid foaming process. The midsole surface is designed with a honeycomb three-dimensional texture, which converts impact force into propulsion force through deformation rebound mechanism, enhancing dynamic response.

Anta's MARSFORM technology is a high-resilience foam particle made from reconstituted TPU, primarily designed for cushioning and rebound, providing a soft and bouncy landing effect. Due to structural optimization, it is lighter than ordinary TPU materials, while also exhibiting stronger abrasion resistance and anti-deterioration properties.

2. Foamed EVA

EVA is the abbreviation for ethylene-vinyl acetate copolymer, a random copolymer composed of nonpolar, crystalline ethylene monomers and strongly polar, amorphous vinyl acetate monomers (also known as VA).

EVA is widely used in shoe midsoles. EVA foam midsoles are soft, elastic, and chemically resistant, but they tend to collapse over time. To improve its performance, different modifiers are usually added during composite foaming. There are many shoe styles using EVA foam midsoles; almost every brand offers them.

Adidas' ADISTAR series uses a dual-density midsole combination. The REPETITOR midsole in the forefoot uses soft foam for a comfortable feel, while the REPETITOR+ material in the heel is a harder EVA material containing 15% recycled materials, which is more resilient and denser, providing stability during heel strikes and suitable for jogging with a heel strike.

Saucony's Cohesion series is its entry-level cushioned running shoe, typically featuring upgraded EVA foam and GRID cushioning technology. Compared to regular EVA, it improves cushioning rebound performance and durability, while also incorporating the GRID mesh cushioning system for enhanced stability.

3. Foamed PEBA

Nylon elastomers are considered the lightest thermoplastic elastomers available. Their synthesis is relatively complex, and production capacity is largely concentrated in the hands of large international manufacturers (such as Arkema), resulting in a relatively high price. They are primarily used in high-end running shoes, hiking boots, ski boots, and similar products.

Nike's ZoomX foam material is made from supercritical PEBA foam, offering excellent cushioning and high-efficiency rebound performance. Reportedly, its energy return is about 15% higher than Adidas' Boost cushioning technology, providing stronger shock absorption and cushioning.

Xtep's XTEP ACE cushioning technology uses PEBA material as its base material, and its pioneering PISA supercritical foaming technology boasts a rebound rate of up to 85%. The Xtep Shadow Pro uses a dual-layer XTEP ACE technology combined with a hollowed-out midsole design, combining material and structure for dual shock absorption, more effectively absorbing ground impact upon landing and reducing the risk of running injuries.

4. Other damping materials

GEL cushioning gel: ASICS' GEL cushioning gel is a cutting-edge technology in the cushioning industry. There are many tests on its cushioning ability, such as an egg falling from more than ten meters onto a GEL pad without any damage, and a ceramic plate wrapped in GEL being hit hard without breaking, etc.

OBCs elastomers: a type of polyolefin block elastomer, which can be considered a special type of POE. It is used as a modifier in EVA composite shoe materials and can also be used as a main component.

P4U material: Peak's Taichi Technology first publicly disclosed the application of this P4U material in footwear materials. It has the ability to change its functional properties according to changes in the human body's movement state. This easily leads one to think of a non-Newtonian fluid, but it is not actually a completely non-Newtonian fluid.

SEBS: PG7 cushioning material, jointly developed by Anta and the Shoe Materials Innovation Laboratory of Sinopec, uses SEBSYH530 modified material as the base material and combines the properties of thermoplastic elastomer (TPE) and EVA. This combination optimizes the shortcomings of traditional EVA, such as hardness, weight, and weak resilience, while retaining the high elasticity and fatigue resistance of TPE.

α-FLEX Intelligent Fluid Material: Hongxing Erke's α-FLEX is a translucent intelligent fluid material that is soft and highly malleable. Numerous nanospheres are freely suspended within it, dynamically sensing pressure and providing intelligent feedback. By incorporating α-FLEX intelligent material into the midsole and employing a particle foaming process, it achieves a responsive and elastic cushioning function.