The ULTRA Otec is a neutral trainer with a performance-fast feel and the substance to handle all of your running. BareFit fits your foot best. CarbonSpan+ is lighter, stronger, and tuned to running. It's everything that plastic isn't. You will notice CarbonSpan+ provides balanced support and a smooth powerful toe-off count. The asymmetrical design matches your foot. Z-bound is a midsole technology, that consists of a lightweight and resilient compound, responsible for the responsive ride. Z-bound has a very high-energy return. The result is less weight and great response.