How do you improve a running shoe that provides endless energy return? By offering even more. The adidas Ultraboost 21 shoe is ultra-comfortable, so extra miles and sprints are effortless. In addition to the Boost technology in the midsole, it features the Linear Energy Push system that enhances momentum with every stride.This product is made with Primeblue, a high-performance recycled material made in part from Parley Ocean Plastic. 50% of the upper is textile, 75% of the textile is made of Primeblue fibre. No virgin polyester. Integrated liner.