In addition to the 360° System, the X Stab Concept (a rigid plastic TPU insert) helps stabilise the heel. This insert is embedded into the compressed EVA and helps stabilise the heel and keep it in position at the back of the shoe. The insert extends out at the sides so that it is covered by the 360° System strap, gently merging with the rest of the shoe at the forefoot. It is used to brace the foot and, along with the injected EVA in the front sole, provides excellent push off.