Sievi AirRacer shoe with BOA® closure. The SieviAir® sole conducts moisture and heat away from the foot, providing more than 30% better breathability through the ventilation ducts in the side of the sole. Sievi’s FlexEnergy absorbs the kinetic energy created, providing over 55% return energy. FlexEnergy is the same ultra light and shock-absorbing sole material that is used in running shoes.