Upgrade your shoes with Superfeet FLEX insoles. An excellent introduction to doctor-recommended Superfeet shape, the special flex design hugs your feet and cradles your heels to help your footwear, and you, feel great. Durable 4mm thick Aerospring™ comfort foam delivers heel-to-toe comfort, while the flexible heel cradle provides structure and stability, reducing stress on feet, ankles and knees. FLEX insoles fit best in athletic footwear. Trim to fit your shoe size.