What is EVA, and why does it matter?
Most of us buy shoes for comfort and performance, but how many know what materials those shoes contain? EVA is a common shoe material—you’ll find it in most pairs in some form or another.
Understanding the different types of EVA and their role in your shoes could help you make better choices when buying running shoes.
Here’s what you should know about it and how it fits your shoes!
What Is EVA?
EVA—ethylene vinyl acetate—is a foam-like material created by mixing plastic-type substances ethylene and vinyl acetate. Vinyl acetate makes up between 10 and 40 percent of EVA, the remainder being ethylene.
It may be compared to rubber, with a natural stretch and bounce. It can also be produced in varying degrees of softness, dictated by the amount of vinyl acetate present—the more vinyl acetate, the higher the quality of EVA.
An important factor in EVA—and the thing that takes it from a simple plastic mixer to an actual foam—is the process of “blowing,” adding small bubbles into the plastic mixture, and turning it into foam.
You can find EVA in many products—not just shoes! While it’s present in almost every pair of running shoes and casual shoes, it’s also found in things like yoga mats, packaging, insulation materials, life jackets, bicycle seats, and boxing gloves.
If you’re curious about where it fits into shoes, it’s used in the midsole and outsole—the parts directly underneath your feet.
The Different Types of EVA
There are three different types of EVA, categorized by their different levels of vinyl acetate.
Vinyl-Acetate Modified Polyethylene
This type of EVA contains only around 4 percent vinyl acetate. It can feel hard and brittle, so it’s not usually used in shoes.
The second kind of EVA contains a medium level of vinyl acetate—between 4 percent and 30 percent. This is similar to rubber, so it’s used in some shoes.
Ethylene-Vinyl Acetate Rubber
This type of EVA contains around 30 to 40 percent vinyl acetate. These are the higher quality types and have more softness, making them a good shoe choice.
Manufacturing Process of EVA Foam
Aside from different types of EVA, there are also different manufacturing processes to get to the final product. Compression- and injection-molded EVA midsoles or outsoles are found in almost all running shoes.
Compression-Molded EVA (CMEVA)
Compression-molding uses a metal block to create specifically-shaped pieces of EVA. The already-expanded EVA is placed into the mold, then heated and compressed. As it heats up the EVA expands, taking on the exact shape of the mold—including any small etchings on the inside.
Once cooled, the EVA piece—now a midsole or outsole—is removed, ready to be placed into a shoe design. The downside of compression molding is that it leads to waste because you’re using a cut-off piece of EVA. However, it produces a much better quality design than injection molding.
Injection-Molded EVA (IMEVA)
During injection molding, the EVA mixture and a blowing agent—the thing that creates the foam bubbles in the mixture—are placed inside a mold. Unlike compression molding, this mold is about half the size of the finished product.
It also has certain markings on the inside of the mold, which will transfer to the end piece of EVA. The mold is heated and cooled, and when it’s opened, the piece of EVA expands suddenly, almost bouncing out of the mold.
The end result is a piece of midsole or outsole foam that’s the right size for whatever shoe it’s designed for, created out of a smaller mold. The bonus here is that there’s no waste—it only uses the exact amount of EVA necessary.
How Is EVA Used in Shoes?
EVA is common in both athletic shoes and casual sneakers. Here’s where you can find it in your favorite pair of shoes.
Insoles are the removable layers inside your shoes. They provide arch support, add extra cushioning, and can provide a better fit. Depending on the insole, they may be made from EVA, but some are made of leather, memory foam, or other materials.
Midsoles are commonly made of EVA. In fact, most shoe brands have their own proprietary EVA material, like New Balance’s Fresh Foam or Hoka’s CMEVA foam blends.
The outsole is also commonly made of EVA, with a layer of firmer, more robust rubber underneath to take on the ground. This is where you’re most likely to see those etchings from the manufacturing process—in the unique shape and markings around the outer edge of the outsole.
Benefits of EVA In Shoes
There’s a reason most running shoes—and a ton of casual shoes—use EVA in their midsoles and outsoles. Here are some of the biggest benefits.
EVA offers all the comfort and performance benefits without weighing you down. It’s incredibly lightweight, which is particularly great for running shoes as it won’t hamper your speed.
It Provides Cushioning and Comfort
EVA—the right kind—is softer and cushier than rubber. This means they’ll mold to your feet and provide excellent comfort and cushioning, while still providing the bounce you need to perform.
Offers Support and Stability
While EVA is soft and cushioned, it’s not without support. The firmness adds a level of support and stability underfoot without being intrusive. This is handy for casual and running shoes, but it’s particularly helpful in athletic footwear.
It Helps with Shock Absorption
One of the great things about EVA is that it absorbs shock, reducing the impact on your feet every time you take a step. This is invaluable for a high-impact sport like running, protecting your feet every time you run.
Is EVA or PU Better?
Polyurethane is another common material used in shoes, both in midsoles and outsoles. It’s more common in sneakers and casual shoes than in athletic shoes.
EVA is light, spongy, and great for cushioning your feet. PU is denser than EVA but also heavier, so it’s more popular on non-sport shoes. While it provides good support over time where EVA tends to flatten, it’s not nearly as comfortable to run in.
As for which is better, that comes down to your reason for wearing the shoes. If you’re after a sleek, speedy pair of running shoes, then EVA is definitely the better bet. But if you’re looking for a robust and long-lasting pair of casual shoes, PU is a good choice.
How Long Does EVA Material Last?
While EVA is excellent for comfort and performance, its downside is its relatively short lifespan. While shoe manufacturers do what they can to extend the lifespan of their midsoles and outsoles, most running shoes last 400 to 500 miles.
As EVA is made up of air-infused material, the more they get compressed over time, the harder it becomes for them to “bounce back” and retain their shape. After a certain number of miles, they just can’t return, causing the midsole to stay flatter… Which means it’s no longer providing the support and cushioning it was in the beginning.
You can expect 400 to 500 miles out of your EVA shoes, but assessing them on a shoe-by-shoe basis is important. If you get to 300 miles and your shoes aren’t providing the right kind of support anymore, it’s time for a replacement.
On the other hand, if you’re at 600 miles and they’re still going strong, you don’t need to get a new pair just yet. Assess as you go.
Factors to Consider When Choosing Shoes With EVA
Not all EVA shoes are the same. When looking for a new pair, here’s what you should be considering:
- The right arch support for your foot
- A matching foot shape to yours
- Softness/firmness that feels comfortable
- Cushioning that supports your goal
- Support features you may need
It’s a good idea to base your chosen shoe on your goals. Are you planning on running long distances, a few times a week? You might prefer a softer EVA foam that effectively absorbs shock on those longer runs.
Or are you going to be doing more speedwork? In that case, you may want a slightly firmer EVA shoe, with a thinner cushion that’s as lightweight as possible.
On the other hand, if you’re just looking for a casual shoe, it’s all about comfort. What feels the best to you? Choose something that’s the best combination of comfort and style!