Ultra Boost 21 sneakers Thanks to an improved Boost midsole, adidas' Ultra Boost 21 sneakers are the lightest to date. Bursts of violet accent the heel and signature 3-Stripes logo, standing out against a black-hued Primeknit and textile backdrop. Underfoot, the Continental™ rubber outsole offers enhanced comfort and durability.  Imported Composition Sole: Rubber 100% Outer: Fabric 100% Lining: Fabric 100%