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.