Upgrade your shoes with Superfeet FLEXthin insoles. An excellent introduction to the doctor-recommended Superfeet shape, the special flex design hugs your feet and cradles your heels to help your footwear, and you, feel great. Durable 3mm Aerospring™ comfort foam delivers heel-to-toe comfort, while the flexible heel cradle provides structure and stability, reducing stress on feet, ankles and knees. FLEXthin insoles are designed to fit well in slim-fitting footwear, even some without removable insoles. Trim to fit your shoe size.