Keep on running!
By Luis Rodriguez, DuPont Performance Polymers, US
Three models of running shoes from the U.S. footwear company SKECHERS feature its Kinetic Return System for forward propulsion, a system that relies on the strength and flexibility of DuPont™ Hytrel® thermoplastic polyester elastomer.
Wearers of three performance fitness models of SKECHERS running and training shoes can benefit from an explosive turn of pace thanks to the Kinetic Return System (KRS) embedded within their soles. Developed
in-house and exclusive to SKECHERS footwear, the KRS combines the strength and flexibility of Hytrel® thermoplastic polyester elastomer with the efficiency of an elliptical shape to deflect and convert impact forces and elastic energy into forward motion, as the centre of the foot strikes the ground.
According to SKECHERS' Vice President of Fitness Technical Development, Kurt Stockbridge, the DuPont material has been key to realizing its Kinetic Return concept. "We started with the idea of the Kinetic Return System and effectively built the shoes around it, so there was a lot riding on the system to perform in order to set these shoes apart from what was currently in the marketplace," he recalls. The development team at SKECHERS knew from experience that other materials such as thermoplastic polyurethane would not provide the energy return they were looking for, as well as lacking other key properties. "It was critical that the chosen material not suffer from cyclical fatigue, compression set, energy loss, or cracking over time since the KRS would be cycled hundreds of thousands of times over the life of the product," continues Stockbridge. "Once we became more familiar with Hytrel® we knew we had the ideal match for what we were trying to accomplish."
The enthusiastic response of DuPont colleagues in the U.S. to the project, as well as access to similar applications in Hytrel® requiring high flexibility and durability, helped reassure SKECHERS in its choice of both material and development partner. Extensive product testing followed: a wear test, typically lasting between 10 and 12 weeks, was carried out for each model of shoe and by athletes matching its intended usage profile. The primary focus of these tests was the dynamic response and durability of the shoes, as well as their biomechanical and mechanical performance. The results relating to the KRS were very positive in all regards.
The global support available from DuPont—both to the SKECHERS team in the U.S. and to the molder in China—was also striking. "We were very impressed with the team at DuPont," confirms Stockbridge. "The fact that they have very strict processing and molding standards, and were willing to send colleagues to our mold shop in China, not only to teach them how to mold Hytrel® but to put quality assurance measures in place, was critical to our success. They also offered their expertise during the design phase to help ensure our KRS would perform as intended, which was a big help to us since we lacked experience with Hytrel® for this specific application."
The Kinetic Return System with Hytrel® is currently used in the SKECHERS ProSpeed running shoe, the SKECHERS Pro-TR training shoe and the SKECHERS Pro Resistance™ shoe—a high resistance and support shoe designed for distance and power. "These three models define the best of what we have to offer due to the unique benefits of the KRS returning energy to the athlete," concludes Stockbridge. "Runners love the springy feel and smooth transition the KRS provides, which generally makes their workouts more enjoyable."
All SKECHERS models are available internationally through authorized retail, department and outlet stores. SKECHERS' extensive footwear collection is available online at www.skechers.com.