BOOST midsole Lace closure BOOST midsole provides additional energy to your feet with every step Adidas PRIMEKNIT textile upper Say hello to supreme energy return. We remade our high-energy running shoes with a 360 fit improvement. The Ultraboost 22 has a narrower heel fit and lower instep curve to reduce heel slippage and help avoid blisters, plus the medial outsole pattern has been refined for a smoother ride. Throw in the foot-hugging adidas PRIMEKNIT and incredible energy return of BOOST, and you get an ultra-comfortable shoe for any distance.