Running Shoe Series: adidas UltraBOOST Infographic

Written by: Adam Bible

Illustrated by: Allie Surdovel

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Better cushioning—and more of it—has long been a part of building the ultimate running shoe. However, the material traditionally used for this cushioning, EVA (ethylene vinyl acetate) foam, isn't very flexible. So for shoe manufacturers who use EVA in the sole and want to make it lighter and more malleable, they have to remove material, often by cutting slots in it.

In 2006 the materials gurus at chemistry giant BASF and Adidas started playing around with particles of expanded thermoplastic polyurethane (E-TPU) to try and solve this problem. Shaped like big rice grains, the plastic capsules had properties that would make for great running shoe cushioning—soft, flexible, highly elastic, and easily compressible.

Knowing this, the researchers welded thousands of them together using steam and pressure. They then formed a midsole out of the material and found that all the capsules bound together created a unique cell structure that is highly elastic.source This responsiveness allows the foam to return back to its original form when compressed. That process releases energy efficiently back to the runner when you strike the ground and then lift your foot up again.

Adidas called this new material Energy Boost. Released in 2013, shoes made with a Boost midsole have become a hit for runners and lifestyle aficionados alike. There have been several iterations of the Boost technology, but with the introduction of Ultra Boost in 2015 they aimed to “provide the greatest running experience ever."

So how'd they do it? The updated midsole material features 20 percent more E-TPU capsules packed in than any previous version, meaning even more cushioning and energy return. Adidas also redesigned the heel to more comfortably cradle the foot, allowing the shoe to adjust during compression to work more naturally with the movements of the runner's Achilles tendon. Other additions included a new sock liner that adapts to individual foot forms and a TORSION® SYSTEM in the shoe's base that gives runners a more stable and smoother run.

Comfortable Feel

With the relatively hard EVA (ethylene vinyl acetate) midsole found in many shoes, you end up running on top of it. But with Ultra Boost, although you sink deeper into the foam, it still offers support. Thus, a soft sole no longer means unstable performance.

Ultra Boost also gives you a host of benefits in one material—a ton of cushioning without a lot of height, durability for long-term and consistent performance, and increased ability to resist deformation or any other compromises in compression due to the ambient temperature while running—it stays softer in the cold and stiffer in the heat.

Flexible Stretch

In addition to reinventing the midsole material, Adidas also redesigned the outer sole, coming up with a grid-type rubber pattern they call Stretchweb. This helps the UltraBoost midsole keep its shape. The unique tread design works like hundreds of rubber bands, stretching and moving to adapt to the way different people's feet flex and move while running. This extra flexibility when the sole hits the ground helps unleash the full potential of your body by letting the foot spread out wider with each stride, making for a more stable and natural gait.

Energy Return

Each part of the Ultra Boost system was designed to give more energy back to the runner. The midsole itself, which has 3,000 E-TPU capsules, provides more compression to bounce back more efficiently.13 The Stretchweb sole also expands and prevents the foam from deforming when you land, which allows for more flexibility and elasticity. It then contracts like a rubber band to help the foam spring back into shape, simultaneously returning more energy to the midsole and, ultimately, into your run.

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