These researches aimed at bringing significant and useful information regarding the morphologies and relaxation behaviour of PP/EPDM blends as detailed morphological studies of such uncrosslinked blends are still lacking in the literature. This work allowed a fruitful study of the correlation between their morphology and final mechanical properties, especially concerning their relaxation behaviour. In particular, among all the expected morphologies, the co-continuity is virtually undescribed in the literature whereas it is surely one of the most interesting one regarding the confinement effect of two continuous phases having such a low interfacial tension. The experimental conditions leading to such an atypical morphology have been thoroughly described, and its final properties have shown amazing results especially regarding the relaxation and strain recovery behaviours encountered during compression set experiments. As a matter of fact, these experiments highlighted interesting industrial properties related to such a particular morphology: uncrosslinked co-continuous blends reveal a final strain recovery of nearly 40% after a 25% strain applied for 10 h at 100 degrees C which could be discussed on the basis of several physical and theological considerations. Additionally, the study of the stabilization of such a morphology has also brought interesting results. Finally, we have also studied the influence of hydrophilic and hydrophobic silica nanoparticles on such a specific morphology and its correlated compression set properties. (C) 2008 Elsevier B.V. All rights reserved.