High potential of microcellular PP motivated to do investigation on foamability of blends, composite and nanocomposites of PP. Rheology of PP with varying molecular weight and amorphous content directly directs the foamability. For foaming of PP/HMSPP blends the foam density reduced with increase of branch content of PP and for PP/crosslinked or uncrosslinked elastomer blends the elastomer particle size was very important for foaming. Blends interface acted as the nucleating site for foaming and interfacial interaction of raw materials had important role in foamability. The introduction of crosslinked elastomer into the polypropylene matrix improved the foamability of polypropylene up to a certain limit and then deteriorated. For PP/fiber system although, the incorporation of fiber increased the foamability of PP; a significant insight could be observed for the uncompatibilized and compatibilized composites in terms of polymer-fiber interaction, which eventually governed the foamability. The compatibilized composites showed lower density foams with smaller cell sizes as compared to the uncompatibilized composites. The effect of rheological influence on the development of microstructure in polypropylene/clay nanocomposites vis-à-vis foamability of the nanocomposites was identified. With the increase in clay loading, cell density increased; furthermore, with an increase in saturation time, there was a phenomenal decrease in expansion ratio of neat polypropylene due to CO2-induced crystallization which could be mitigated by the incorporation of nanoclay into the polypropylene matrix. The objective of introducing HNT and CNT was to facilitate the heterogeneous nucleation for foaming and improvement of melt strength of polypropylene. A substantial amount of foaming has also been performed with UHMWPE with variable molecular weights and in presence of other processing aids, where molecular weight and rheology was found to be crucial.