Cushion: The MVP of Running Shoe Technology

The most important component of your faithful running shoe is the cushioned midsole. The midsole is the warrior protecting your feet from the exhausting impact of the road. Simply, the cushioned midsole provides protection and rebound.

Role of the Midsole

So why is the midsole so important? According to CoolRunning.com the midsole:

The cushion-y midsole is one of the most important parts of a good running shoe, therefore the foam that makes up the midsole is highly influential for the comfort and performance of the shoe. Two foam technologies have dominated running shoe design over the past decade: EVA and PU.

EVA
EVA is a copolymer or cross-linked foam made of ethylene and vinyl acetate. Hundreds of foam cells containing air or gas make up EVA foam. More simply, CoolRunning.com describes EVA:

EVA is the darling of running shoes. – It is light, it is flexible – and it has a great disposition as a cushioning material. If it were human, you would invite it to your next after race party. But like any good thing, it just doesn’t last forever. Over time and repeated impacts EVA tends to compress and lose some of its rebound or resilience. Runners notice this and say their shoes feel “flat”. The technical term would be the foam has taken a “compression set”.

PU

PU or polyurethane is a stronger, heavier version of EVA. In your running shoe, it behaves similarly to EVA, except that it takes significantly longer for it to feel flat, or take a “compression set.” It’s fantastically durable, but provides less spring than EVA. If you’re running shoe midsole is made primarily of PU, you can rest assured your shoe will last a long time, but it may start feeling heavy. As your shoe ages, the ‘bounce’ it provides will sharply decline.

March 15, 2006. Sneakers.