The result? 4% more forefoot energy return, compared to Ultraboost 21 for women. The adidas PRIMEKNIT upper includes a narrower heel fit, designed to avoid heel slip and blisters. You'll be riding on a BOOST midsole with a Linear Energy Push system. The shoe's upper is made with yarn containing 50% Parley Ocean Plastic —? reimagined plastic waste, intercepted on remote islands, beaches, coastal communities and shorelines, preventing it from polluting our ocean.