Running shoe
EVA foam forms a light cushioning layer between the shoe upper and outsole.
Material
EVA-based foam midsole: EVA
Material selection rationale
- Cellular cushioning
- Gas-filled cells compress under a step.
- Flexible polymer
- Allows the foam layer to bend with the shoe.
- Compression and recovery
- Cells compress during loading and recover to a formulation-dependent extent; foam density and repeated compression affect cushioning over time.
How it becomes a product
- Compound and foam: An EVA-based formulation is mixed and expanded into foam. The selected compound is foamed and shaped; cell size, density and any crosslinking are controlled before assembly with upper and outsole.
- Shape and assemble: The foam is moulded or cut into a midsole and joined to the other shoe components.
Preparation routes
Ethene and vinyl acetate route
Addition copolymerisation. Both monomers add through their carbon–carbon double bonds to form a chain containing ethene-derived and vinyl-acetate-derived units. Both double bonds participate, while acetate groups stay attached to the vinyl-acetate-derived segments. Changing their proportion changes flexibility without a separate PVC-style plasticiser.
Industrial initiators and reaction controls support chain growth. Foaming agents, adhesive waxes and tackifiers are added in later product-formulation steps. Neither the foam gas nor an adhesive tackifier belongs in the required monomer pair.
From ethene and ethanoic acid to vinyl acetate
- Ethene + Ethanoic acid + Oxygen → Vinyl acetate
Ethene, ethanoic acid and oxygen react in a catalytic gas-phase process to make vinyl acetate. Unreacted ethene and acid are recovered, and the monomer is refined. The product retains a polymerisable vinyl group alongside its ester group. It is chemically distinct from ethyl ethanoate, which has a saturated ethyl group.
- Vinyl acetate monomer: reaction, feedstock recovery and refiningLOTTE INEOS Chemical
- Vinyl acetate monomerCelanese