Linear/branched PP blends at various ratios were used as the matrix for thermoplastic olefin (TPO) compounds, containing an ethylene-octene copolymer dispersed phase. A detailed investigation of the physical properties of these blends revealed that addition of branched PP (BPP) resulted in improved stiffness and flexural properties. Given that the phase morphology of the blends and the interfacial tension between their components remained virtually unaffected, these improvements are attributed to the higher stiffness of the BPP-containing matrices. Talc-filled TPOs containing branched PPs exhibited further improvements in the stiffness and flexural properties. An investigation into the bubble growth process during foaming using a batch foaming simulaiton system revealed that the presence of BPP resulted in a slight delay in cell nucleation, whereas the rate of bubble growth was not significantly altered. (c) Wiley Periodicals, Inc.