What is the Difference Between EVA and Polyurethane Midsoles?
Most shoe or boot midsoles on the market today are made from EVA or polyurethane. There are many misconceptions with each and they are drastically different from one another. What is the difference between the two?
Polyurethane is an organic polymer held together by inserting urethane urethane which forms the structure. It makes for a very highly resilient foam compound. This material is used in many every day objects such as seals, gaskets, skateboard wheels due to its strength and ease of fabrication. One of the qualities it makes polyurethane a desirable material for footwear is its high resiliency meaning that it does not have a tendency to flatten or compress over time. This desirable quality comes at the cost of a heavier weight than alternative foam compounds since polyurethane has a higher specific weight and density than most other foam rubber alternatives used in the midsoles of shoes and boots today. The real benefit of polyurethane midsoles are their long-life and durability since it does not compress over time and has no memory. It it typically a more expensive material and used in higher grade brands and models of footwear. Again, it's primary benefit is it will not conform or have a memory like other foams on the market.
EVA stands for ethel vinyl acetate. It is a man-made material that is considered foam. EVA materials consist of thousands of tiny bubbles joined together that hold air. When compressed, these bubbles provide cushioning and shock absorption, making EVA an ideal material for performance footwear. The primary advantage of EVA as compared to other shock attenuating materials is it is light. It has a low density and is lightweight so it it is ideal for some types of footwear where weight is a factor. The drawback to EVA midsoles is that over time, the tiny bubbles that provide the cushioning start to lose some of the air and become compressed. Over time, a footwear product made from EVA will lose it's cushioning and support. This is why athletic shoes, especially high impact shoes such as running shoes, are recommended to be replaced every 3 to 6 months.
Which of the two is better? It really depends on the application and type of footwear. If you're looking for the absolute lightest shoe or boot around, then EVA would be the obvious choice to maximize performance. It will also generally be cheaper than most of the comparable polyurethane models. On the other hand, if the requirement for your footwear is longevity and you aren't concerned too much about weight, then polyurethane would be the better choice. and willing to pay more then polyurethane is the better choice this can be observed as a flattening or compression of the men this phenomenon will be noticed usually when the ware finds that the footwear overtime loses its balance