Polymer foams for personal protection: cushions, shoes and helmets

Three areas, where polymer foam products are used in personal protection, are reviewed to contrast the foam micromechanisms and the use of Finite Element Analysis (FEA) for engineering design. For flexible open-cell foams used for seating cushions, the main deformation mechanism is cell edge bending; regular cell models can predict much of the compressive response. Hyperelastic FEA models can then predict the forces for foam indentation. For flexible closed-cell foams used in shoe midsoles, cell air compression dominates the response; diffusive air loss leads to foam deterioration with use. Hyperelastic FEA models can predict the interaction between the foam and the heelpad. Finally, for rigid closed-cell foams used in helmets, the permanent stretching and wrinkling of cell faces dominates the response. Crushable foam FEA models, which consider the yield surface and hardening, predict different responses for impacts on the road and on a kerbstone.