The sheer volume of specialized vocabulary that you can come across when you’re in the market for running shoes can be daunting to say the least. There is an abundance of terms out there, many of which are highly technical.
And yet, the endless terminology and marketing jargon is no more confusing than when it comes to naming rubbers and foams. EVA is one of these terms, and happens to be one of the most popular as well when looking around at running shoes.
Below, we are going to take a look at what EVA material is exactly, and what benefits it has on your running. EVA material is found in some of the best running shoes of today.
A Brief Overview of EVA
EVA – or ethylene vinyl acetate – is a copolymer, or the joining of two plastics in the same polymer chain. In the case of EVA, these two plastics are ethylene and vinyl acetate. You might hear people refer to PEVA as well, which is poly-ethylene-vinyl-acetate, but it’s all the same stuff.
EVA is used to produce materials that are rubber-like in flexibility and softness. It can be clear or glossy, as well as resistant to UV radiation, stress cracking, and damage resulting from extreme temperatures.
To put it plainly, EVA is one of the most useful synthetic materials that is used in manufacturing, and has applications far beyond the shoe industry. It is often pitted against rubber and vinyl polymer as a material for electrical applications as well.
The Three Types of EVA
There are three types of EVA, generally speaking, and they differ based on the volume of vinyl acetate that they contain. Let’s take a look at these three types now.
The first kind of EVA is the thermoplastic ethylene-vinyl acetate copolymer, which has a medium vinyl acetate level, ranging between 4% to 30%. This type is a thermoplastic elastomer material that is unvulcanized, and that shares many of the same properties as rubber.
Vinyl-acetate modified polyethylene
This next variation of EVA, which is more similar to polyethylene than to EVA, has a low vinyl-acetate proportion – roughly around 4%. This type of EVA is processed in the same way that a thermoplastic material is, and is generally considered non-toxic.
Ethylene-vinyl acetate rubber
Lastly, ethylene-vinyl acetate rubber is an EVA copolymer that has a high concentration of vinyl acetate, usually of above 40%.
EVA in Shoe Manufacturing
If you are an experienced runner or have done any research into running and running shoes, then you may know that EVA is the most common cushioning material used in the construction of athletic footwear midsoles. You’ll find this material in running shoes, basketball shoes, and most other kinds of athletic footwear, thanks to its lightweight nature and ability to resist compression.
EVA is also remarkably easy to manufacture in a range of colors, and is even easier to form. You’ll find it used on both the cheapest of sneakers and the most exclusive pro-footwear on the market.
Why Have EVA Midsoles?
Now that we understand what EVA is, we can start to take a look at why you should consider picking shoes that have EVA midsoles.
EVA is used mostly for the midsole – which is the layer that is found between the upper and the outsole. The midsole is the part of the shoe that is responsible for energy return and cushioning, which adds efficiency, comfort, and protection to the shoe. When it is well-constructed, the midsole follows the contour of the foot, which makes the maneuverability of EVA an obvious choice for running shoes.
Stability is another essential feature that is provided by midsoles, and is the same reason that midsoles have to be constructed from materials that are capable of handling pressure. Furthermore, the midsole must be able to handle pressure from the weight of the user, or from the surface that they are running from.
Again, this is what makes EVA an ideal material for the construction of midsoles.
EVA in Soles
EVA is not just used for the making of midsoles, contrary to popular belief. Nowadays, the use of EVA in the manufacturing of shoes is more varied than ever before, and advances in the field have allowed the material to make its way to different parts of the shoe.
EVA is now found in the insole and outsole of most shoes, and not just of those used for running; you’ll find EVA in your household slippers, your favorite sneakers, and more.
Why is this?
Well, for starters, EVA soles are highly resistant to the corrosion that is caused by fats, sea water, chemicals, and oil. It is also considered a safe and environmentally-friendly material, thanks to its non-toxic and anti-bacterial properties.
Like we mentioned before, EVA is an excellent option for vibration reduction and cushioning thanks to its tensile strength, resistance, and toughness. Furthermore, it offers great insulation in colder temperatures, which is why you’ll often find EVA in hiking boots.
Nothing in this world is perfect, and the same goes for EVA. EVA – and really any foam – is made up of thousands of small bubbles that trap air. This is the property that allows it to absorb shock and cushion your feet, but is also the material’s biggest downside when used in shoes.
Over time, no matter what, bubbles compress and pop. This is why most runners complain about their shoes eventually feeling flat, and is also the reason why most shoe manufacturers suggest a 300 to 500-mile lifespan for the running shoes. To put it simply, EVA has a short life.
However, manufacturers of high-end athletic footwear have found a way to make the material last longer: molding. This process involves using a pressurized mold to compress the EVA material in such a way that the midsoles form a thick skin, making the soles far more durable.
This is quite an expensive process, which means that any running shoes that are made using EVA molding are going to be quite a bit more expensive.
Marko is a recreational runner (and a techie) that has completed a full-distance trail marathon from Australia. He is the lead writer at JogTunes and spends his off-time time testing different running shoes and GPS watches.