Free is to cut the Phylon sole according to people's foot shape to provide necessary protection for feet, and at the same time provide flexibility by imitating barefoot movement, exercise the muscles of feet and legs, and wear it like thick socks. Zoom uses Zoom Air, which is close to the ground and has fast response, but the shock absorption is not as good as Max's. Max uses Max Air, which provides excellent shock absorption through large air volume, but it is high from the ground and slightly less stable. Lunar uses the lunar material jointly developed by Nike and NASA, which can not only absorb vibration, but also release elastic potential energy to the next action, and find a balance between stability and shock absorption.