Can someone explain to me the difference between these terms when talking about midsoles for running shoes? I see these terms used interchangebly when talking about midsoles but am always confused. If EVA is used because of its cushioning properties, wouldnt compressing it just make for a less cushioned shoe? Also,is the EVA they use in midsoles the same as the ones used in orthotics?
I believe one is just cut from sheets of foam and looks like the old school type of shoes where you could actually see the "raw" surface on the outside.
Compression molded is formed in a mold so that the outside is shaped and smooth.
Compression molded is just contained while the foam expands to the shape of the shoe last.
EVA is just the term for the substance, not the form that it actually comes in.
EVA is Ethyl Vinyl Acetate. It's basically molded and injected with air to create different densities. The less dense it is the more cushioned it's going to feel. It will also be lighter in weight. Often you will see "dual density" midsoles, where a plug of EVA is more dense to help prevent pronation, but won't add a ton of weight to the shoe.
The lighter stuff with the open exterior breaks down much faster because all the tiny bubbles can pop and eventually all the contained air can leak out.
Compression molded lasts longer because it is basically sealed on the outside.
"Ethylene"
thanks, I think I got it. It sounds like compression molded just forms the "skin" of the sole and doesnt really effect the cushioning properties of the midsole.