At constant interfacial adhesion, the toughness of plastic– rubber blends measured at low speeds of deformation is a function of morphological parameters, i.e. rubber particlesize, volume fraction and particle spatial distribution parameter. Muratoglu and coworkers [3] demonstrated that there is a substantial influence of both rubber particle size and volume fraction on the elongation-at-break and toughness of nylon 6-rubber blends. The toughness (defined as the area under the stress–strain curve to break) was found to increase with increasing rubber content for a constant rubber particle size and with decreasing rubber particle size for a constant rubber content. Takaki and coworkers [4] reported that the effects of both the size and volume fraction of methyl methacrylate–butadiene–styrene graft copolymer (MBS) particles on the elongation-at-break and the toughness of poly(vinyl chloride) (PVC)–MBS blends can be combined into the effect of a single parameter, namely the matrix ligament thickness. These properties were found to increase with decreasing matrix ligament thickness. Kim and coworkers [5] reported that the rubber particle spatial distribution has a substantial influence on the elongation-at-break values of styrene–acrylonitrile copolymer (SAN)–rubber blends.