The interfacial tension between the components should be relatively low to achieve a good and fine dispersion of the rubber phase. The interfacial tension between PP and EPDM is relatively low. Therefore, this blend does not require compatibilisation with a block or graft copolymer in order to generate a finely dispersed rubber phase and a good interfacial adhesion between the two phases. Furthermore, as a result of the vulcanisation process, the crosslinked rubber particles are relatively resistant towards coalescence upon further melt-processing. In the case of thermoplastic/rubber combinations with a high interfacial tension between the components, it is necessary to compatibilise the blend in order to generate a fine dispersion of the rubber phase. Compatibilisation is usually achieved by using a thermoplastic and a rubber with functional groups that can react with each other during melt-mixing to form a block or graft copolymer at the interface between the phases [2] and [8].