Medium arch signature Superfeet shape adds stability and comfort to your shoes, reducing stress on feet, ankles, knees, and back. Improves efficiency, reduces fatigue, and supports every step. Responsive EVOLyte® carbon fiber cap and a thin layer of Aerospring™ Rebound comfort foam for a versatile fit combine to create smooth and efficient energy transfer throughout your gait, from foot strike to toe-off. Made to replace the removable liner in moderate to tight-fitting shoes.