In this paper, a study on the batch processing and characterization of microcellular foamed high-density polyethylene/isotactic polypropylene (HDPE/iPP) blends is reported. A microcellular plastic is a foamed polymer with a cell density greater than 109 cells/cm(3) and fully grown cells smaller than 10 mu m. Recent studies have shown that the morphology and crystallinity of semicrystalline polymers have a great influence on the solubility and diffusivity of the blowing agent and on the cellular structure of the resulting foam in microcellular batch processing. In this research, blends of HDPE and iPP were used to produce materials with variety of crystalline and phase morphologies to enhance the subsequent microcellular foaming. It was possible to produce much finer and more uniform foams with the blends than with neat HDPE and iPP. Moreover, the mechanical properties and in particular the impact strength of the blends were significantly improved by foaming.