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.