In order to investigate the effect of clay particles on the cellular structure of polyethylene (PE) foam with different clay contents and to confirm the expected synergistic potential between nanocomposites and microcellular foams, a study of batch and continuous foaming processes with PE/clay nanocomposites was conducted using PBAs. A batch foaming process using HDPE/clay nanocomposites produced a very successful nanocellular structure with a high cell density, 10¹³ cells/cm³, and an average cell size that was substantially less than 1 μm. The effects of blowing agent type and content, die geometry, clay content and dispersion on the foamability during the continuous extrusion process were studied in detail. Also, this study presents the optimum content of clay required to achieve high quality microcellular LDPE/clay nanocomposite foams when blown with CO₂. Moreover, the effects of clay dispersion on mechanical and flame retardant properties were investigated.