The morphology of blends of polypropylene (PP), poly(styrene-co-acrylonitrile) (SAN) and barium sulphate (BaSO4) filler was studied as a function of filler particle size and amount and type of maleic anhydride-grafted polypropylene (PP-g-MAH) in the polypropylene matrix. The methods employed were scanning electron microscopy (SEM), dynamic mechanical analysis (DMA) in the solid state and a theoretical model using a core shell model structure. The study showed the possibility of controlling the phase in which the filler is occluded as a function of the chemical character of the PP matrix and the filler particle size. The morphology and dynamical mechanical properties vary in a systematic way, related to the location of the filler in the blends. Theoretical calculations supported the experimental observations.