The heart of the MXT-C3 sole is the Smart Memory Spring. Engineered by the Impact Research Technology Group for Active walkers, its MXT-C3 sole's primary shock absorber has been specially calibrated and placed within the sole housing to create a one of a kind reciprocal shock absorber system that absorbs impact and propels you forward. This sole delivers the highest Forward Thrust Rating (FTR 22%) of any Gravity Defyer footwear. Two secondary springs serve as stabilizers to support the primary spring and reduce yaw in the footwear. Stay cool and refreshed Though this sole is most recognized for its distinctive wedge shaped sole, there are other secrets hidden inside... The AVS³ ventilation system. --No more hot, sticky, smelly feet.