Polyurethane-foam midsoles in running shoes - impact energy and damping

Most running shoe midsoles are made of ethylene vinyl acetate (EVA) foam although excellent mechanical long-term properties of polyurethane (PU) foam are generally known. The aim of this study was to investigate whether PU foam is applicable as midsole material regarding damping properties. Short-term and long-term mechanical tests were conducted for running shoes with midsoles of either PU or EVA foam using the Hydraulic Impact Test. The results of the short-term testing show that PU midsoles can be adjusted to a wide range of damping properties while EVA midsoles attained good average values. In long-term testing, however, the EVA foams exhibited higher relative changes of damping parameters than the PU materials, which confirms the durability and ageing resistance of PU.