What EVA is
Ethylene vinyl acetate is a copolymer of ethylene and vinyl acetate. The vinyl acetate (VA) content is the main lever: more VA gives a softer, more rubber-like and more flexible polymer, less VA gives a stiffer, more polyethylene-like one. Footwear grades typically sit in the mid range of VA content, then get tuned further with fillers, cross-linkers and other polymers blended in.
On its own, solid EVA is far too dense for a midsole. Its value comes from foaming it into a closed-cell structure that is mostly gas by volume.
How EVA midsoles are made
EVA is compounded with a chemical blowing agent, a cross-linking agent (usually a peroxide), activators and pigments. Heat then does two things at once: the peroxide cross-links the polymer chains, and the blowing agent decomposes and releases gas that expands the matrix into cells.
There are three common routes to a finished part:
- Slab or sheet foaming — Large sheets are foamed, then cut, skived and sometimes heat-pressed. Cheapest, but the least control over shape and density.
- Injection molding (IMEVA) — Compound is injected into a heated mold, cross-links and expands as it leaves the mold. Fast cycle times and good for high volume, with less control over final dimensions.
- Compression molding (CMEVA) — A pre-foamed blank is pressed and reheated in a shaped mold. Finer cells, tighter tolerances and crisper sidewall detail. Phylon is the best-known example of this route.
The process choice matters as much as the compound. The same EVA formulation can feel noticeably different depending on cell size, skin thickness and final density.
Cushioning: 8 / 8, Max
EVA's closed cells compress easily under the first part of a footstrike, which spreads load and lowers peak pressure. At low densities this gives the soft, sink-in feel many runners and casual wearers associate with comfort. Density and hardness (usually specified in Asker C for foams) let you dial it from pillowy to firm without changing material family.
Rebound: 4 / 8, Medium
Rebound is how much of the energy put into the foam comes back out. EVA dissipates a large share of that energy as heat rather than returning it, so it feels dampened rather than springy. Resilience is usually checked with a ball rebound test such as ISO 8307. Blending in other polymers or switching to supercritical foaming can lift EVA's rebound, but standard compounds sit well below ETPU and PEBA-based foams.
Durability: 4 / 8, Medium
EVA's weakness is compression set: the permanent loss of thickness after repeated loading, measured with tests such as ASTM D395. Over many kilometres, cell walls fatigue and collapse, the midsole packs out and cushioning drops even when the upper and outsole still look fine. Higher-density and well cross-linked compounds hold up better, but EVA will not match PU or TPU over a long service life.
Where EVA is used
- Running and training shoes — entry and mid-price models, and as a carrier or stabilising layer around premium foams.
- Lifestyle sneakers — light, comfortable and easy to mold into chunky shapes and colorways.
- Sandals and slides — often as one-piece injected EVA that serves as both midsole and outsole.
- Kids' footwear — low weight matters more than long service life for feet that outgrow shoes quickly.
Designing with EVA
Specify EVA when weight, initial softness and unit cost lead the brief. Be cautious when the shoe must keep its ride over a long service life, carry heavy users, or work in high heat, where cushioning loss shows up early.
Practical ways to get more out of it:
- Raise density or hardness in the heel, where compression set hits hardest.
- Pair a soft EVA top layer with a firmer, more resilient bottom layer in dual-density builds.
- Protect the foam with rubber in high-wear zones rather than leaving EVA exposed to the ground.
- Ask for compression set data, not just hardness, when comparing suppliers.
