In the traffic machines such as the automobile, many thin wall closed section members made of steel are used for the improvement in the collision safety. In these members, the local buckling under compressive stress is mentioned as a main problem. In order to improve the mechanical performance of the member, the technique which fills the inside of closed section with the low-density foaming material is used. In this study, axial compression test and 3-point bending test at the various low deformation velocities from elastic region to plastic collapse were carried out on the composite material which filled the hat type thin-walled cross section member with 2 kinds of epoxy resin foaming material in which the foaming rate (density) is different. Characteristics of the energy absorption for composite member were estimated from the stress contribution ratio of the constructional member. This technique is effective as a simplified estimation method for characteristics of composite member in the design.