The theoretical and experimental bending performance of rigid skin polyurethane foam beams, reinforced with thin walled steel sections, was investigated. The aim was to provide design data for the prediction of vehicle structures made of this composite material during accidents.The theoretical treatment assumes an interfacial shear between the core and the faces of the reinforcement. This method gave good agreement with experimental results when the errors due to cantilever support movements were quantified. It also represents a good basis for an inelastic analysis beyond the yield point of the reinforcement which was also developed. The inelastic analysis also showed good agreement with experimental results.A simple optimisation of the reinforcement geometry based on the experimental data was made. This showed that, for uniaxial bending, the composite beams can be made lighter than the lightest rectangular tube made of the same steel and with the same width to depth ratio.Impact tests showed that the behaviour of composite beams is similar for both static and dynamic loading up to the maximum impact speed tested (10 m/secs).