adidas Ultra Boost ST Running Shoes Engineered Mesh Upper - Incorporating differentiating level of thickness to deliver precision support and adaptability whilst being highly breathable. Primeknit Upper - Stretchable construction around the midfoot that adapts to the foot's natural expansion and helps reduce irritation. Featherweight Sockliner - Adapts to the foot for customised fit and feel. Re-designed Heel - Comfortably cradles the foot and adjusts to the Achilles tendon's natural movements. External Heel Counter - Supports and stabilises the foot through every stride for performance comfort.