Batch-foaming of miscible, immiscible and compatibilized polymer blend systems over a wide compositional range was carried out using carbon dioxide as a physical blowing agent. The resulting foam morphology was characterized by a detailed evaluation of foam density as well as of the cellular parameters. With regard to multiphase blends, transmission electron microscopic observations further provided a detailed insight into the cell wall morphology. The role of the melt-elongational properties and of the glass transition behavior of the various blend systems on the foaming characteristics was systematically elucidated. While the miscible blends showed a simple additivity behavior with regard to their foaming characteristics and properties, a significant influence of the initial blend morphology is demonstrated for the multiphase blends.