These insoles are also characterised by their heel protection that ensures greater stability. Size 4/5.5 man - 5.5/7 woman (US) The Ironman Gel insoles provide comfort and stability to the feet thanks to the special composition of Spenco TPR Performance Gel, a gel formula specifically created to provide an energy return of 44%. The triple density gel absorbs impacts and knocks at the points of the foot that suffer more fatigue.