Shoe manufacturers like touting their unique designs and materials in slick-sounding jargon. Supposedly revolutionary foams, meshes, and knits are major selling points and points of competition between brands.
But such terminology can only take a shoe so far, and how these materials perform out on a run is, quite literally, where the rubber meets the road. And where the rubber meets the road–the outsole of the shoe–there are two major divisions of materials: natural rubber, and synthetics such as ethylene vinyl acetate, or EVA.
Both materials have pros and cons. When you are purchasing a pair of running shoes, you probably have a good idea of where and how the shoes will be used. Are you going for long, slow road miles? Working on speed at the track? Ascending and descending aggressive mountain trails? Answering these questions will clarify what qualities are pros, and which are cons. So…which is better for you? Rubber or EVA?
The Basics of EVA
Ethylene vinyl acetate is a copolymer of vinyl acetate and ethylene. EVA is popular for being rubber-like while also having the ability to be manufactured into materials that boost softness and flexibility.
EVA is pervasive in the athletic shoe world. After all, this material can be quite glossy or clear, can be easily dyed into a rainbow of colors, and resists ultraviolet radiation and cracking from high stress.
EVA can be divided into three categories, depending on the amount of vinyl acetate used.
Vinyl acetate modified polyethylene has the lowest vinyl acetate content, at roughly 4%. The processing of this kind of EVA is similar to the processing method of thermoplastic materials. It is also non-toxic.
On the other hand, thermoplastic ethylene-vinyl acetate contains between 4 and 30% thermoplastic ethylene-vinyl acetate. The result mimics many characteristics of rubber.
Ethylene-vinyl acetate rubber has the highest amount of vinyl acetate of the three. Any EVA made of more than 40% vinyl acetate is classified as ethylene-vinyl acetate rubber.
The Basics of Rubber
Rubber can be categorized two ways: natural and synthetic.
Natural rubber is elastic, very soft, and comfortable for athletic shoes. Its main drawback is that it’s not wear-resistant, meaning it does not last long. Natural rubber is often used for indoor sports shoes.
On the other hand, synthetic rubber can be divided into hard, sticky, carbon, air, environmental protection, and wear-resisting rubber.
- Wear-resisting rubber boasts greater durability due to its toughness and rubber-abrasion resistance. It is often used for classic tennis shoe outsoles.
- Environmental rubber, as its name suggests, is made from recyclable material. The rubber sole of this kind has 10 percent or more of recovered rubber.
- Air rubber provides increased shock absorption. However, this material breaks down easily with constant wear, which is why it is not widely used.
- Sticky rubber boasts high flexibility and can prevent slipping, which is why it’s often used for indoor sports footwear.
- Hard rubber prioritizes wear-resistance and toughness. It also prevents slipping. These virtues are the reason why so many basketball shoes and other hybrid athletic footwear use hard rubber.
- Carbon rubber is an ordinary rubber with a twist: carbon is added to the material. The addition of carbon makes the material resistant to wear, which is why many of running shoes are made from this material.
EVA Sole vs Rubber Sole: Outsoles Matter
Shoes, especially athletic footwear, can feature outsoles made from either sub-natural, recycled, or hot-pressed molded rubber. There is an advantage to using rubber soles: unmatched wear resistance (for obvious reasons, manufacturers of running shoes avoid the softer, less-wear-resistant rubbers). Plus, it extends the contraction stability.
Rubber outsoles have other great qualities, such as being naturally waterproof and bendable. The trade-off is weight. As with many natural vs. synthetic comparisons, the natural material tends to be significantly heavier. Your outsoles will last longer, but your feet will be doing some heavy lifting.
On the other hand, EVA is also very common, and is widely recognized as the best material for the midsoles, where your shoes’ cushioning lives. It is, however, also used for sole liners, outsoles and, in some cases, the whole shoe. EVA provides the best shock-absorbing qualities, which is why big-brand shoe makers like to use it. It is light, very flexible, and has high elasticity. Plus, it can take almost any color.
When it comes to outsoles and a direct comparison to synthetic rubbers, EVA is great too. The primary downside of EVA soles is that they do not last long. As with foam midsoles, the material is prone to compression after a certain number of miles, leaving your shoes feeling flat after prolonged usage.
Which Is Better for Running?
Both materials have their pros and cons. Who wins the battle between EVA and rubber soles for running shoes? There is no straight answer. The better material for you and your shoes depends on the running you do.
Your preference for road running or trail is one place to start deciding. These two styles of shoe differ quite a bit, as the former is used for running on flat surfaces at great distances as well as good speed. On the other hand, trail shoes are good for running on uneven, rocky, and rough terrains.
If you are going for speed, a lighter pair of shoes would be a great choice, and that would lead you to EVA outsoles. On the other hand, if one intends to go for more adventurous terrain, then the rugged wear and grip of trail running shoes might lead you to a rubber sole.
Running long distances at fast paces requires lightness, which rubber outsoles cannot provide. Fortunately, shoes made of EVA outsoles are light, which makes them the better option for road running. Rubber soles are quite heavy, which tend to overwork the feet and legs, and making it harder for pure speed.
On the other hand, EVA soles cannot provide as much protection as the rubber soles, which makes them not-the-best option for trail running.
Choose Depending on Your Need
There are some big differences between EVA and rubber for outer soles for running shoes. Rubber is great for protection and durability on natural surfaces, but it can be quite heavy. EVA is lightweight but does not provide adequate support if used as an outsole for those traversing rocky and rough trails. EVA is excellent for the midsole of trail running shoes, but may not be the best material for external support of feet.