The adidas UltraBoost 21 in 'Core Black' is a performance running shoe that magnificently blends lightweight comfort and improved energy return. It embraces sustainable practices by incorporating Recycled Primeblue materials, including Parley Ocean Plastic, into its construct. The knit upper is further fortified with a midfoot cage and molded heel counter for added stability. Boosting its performance, the shoe is equipped with an optimized Boost midsole that contains 6% more Boost capsules than its predecessor, the UltraBoost 20. This new iteration also introduces a revolutionary Torsion system called Linear Energy Push, which enhances responsiveness during each stride.