Currently a high potential of PP foams in automotive industries motivated to make a comparative study among a series of polypropylene/ gamma irradiated elastomer blends by virtue of varying the irradiation dose and elastomer particle size (achieved by different levels of shear). The effects of gamma irradiation of blends directed towards the crosslinking of elastomer (Vamac Ultra IP). Here different levels of shear were achieved by maintaining different screw speeds in a ThermoHaake Minilab microcompounder for a fixed residence time (mixing time). Foaming was done in a high pressure autoclave at three different temperatures using supercritical CO2 as a blowing agent. The cell structure development mechanism was established and moreover, the irradiation dose optimization as well as the compositional optimization was determined. The density of foams decreased with increasing foaming temperature abiding by the general phenomena of foaming. Furthermore, the elastomer particle size played a very key role on foamability of blends, such as smaller particles gave better foam nucleation and homogeneous cell formation. Blends interface acted as the nucleating site for foaming (captured by SEM) and interfacial interaction of raw materials had very important role either in development in blend morphology as well as in foamability. The introduction of crosslinked elastomer into the polypropylene matrix improved the foamability of polypropylene up to a certain limit and then deteriorated. The absolute and specific tensile modulus of foams obtained from the blend compositions with optimally irradiated elastomer showed an increasing trend with the rise in cell density; whereas, the tensile strength of foams was not sacrificed significantly. The absolute and specific impact strength of the foams also exhibited the increasing trend.