Men’s 8 Womens 9 THE HIGH-STACKED RACE SHOE PACKED WITH PERFORMANCE-DRIVEN FEATURES. Built with innovative technology and designed without the constraints of world race regulations, the Prime X 2 Strung offers more performance-driven features in a single race shoe. It's constructed with a STRUNG upper, a textile innovation that transforms athlete data into a dynamic material tuned to the athlete's needs. Prime X 2 Strung also has 3 layers of LIGHTSTRIKE PRO, in a stack height of 50 mm. With an all-new energy core between two layers of foam, it helps to reduce weight and provide spring in the fore- and midfoot, so you can chase your fastest moment. An outsole featuring Continental compound delivers serious grip on a variety of surfaces.