The mechanical characteristics of foamed plastics, based on commercial foams, were studied by observing the role of cell content (foam and relative densities, dimensions of cell edge and face, cell wall, cell shape, etc.) on stress-strain behavior and deformation mechanisms. It is found that the stress-strain behaviour in compression and tension for PVC commercial foam are different beyond linear elastic deformation since cell wall deformations involve different processes. Cell wall thickness which is directly related to foam density dominates the mechanical properties of plastic foams. The regimes of the stress-strain curve are related to the structure of the foam. The foam deformation structure was identified by SEM micrographs which assisted in the interpretation of deformation mechanisms. The mechanical properties of these plastic foams were also characterized in terms of relative density and the degree to which the cells are open or closed. It is found that relative density was found to be a function of geometric aspects of cell structure such as edge and face connectivity, edge and face thickness, etc, which are critical to the understanding of the mechanical properties.