The goal of this study is to fabricate a soft foam with high cell density and high foam expansion based on thermoplastic polyolefin (TPO), and to supply a potential candidate for soft thermoset foams. It was found that a linear polypropylene (PP)-based TPO foam exhibited very poor cell morphology because of its weak melt strength. Nanoclay was introduced into the TPO to improve its foaming behavior. The extrusion foaming experiments demonstrated that the introduction of 0.5 wt% nanoclay significantly increased the cell morphology and expansion ratio of TPO/clay nanocomposite foams due to the enhanced cell nucleation and the possible cell coalescence suppression at low temperatures. At a high nanoclay content of 2.0 wt%, the cell density and foam expansion of foams increased continuously compared with the 0.5 wt% nanoclay addition. Our study suggested that it was possible to produce soft TPO foams with a well-defined cell structure and high foam expansion using a continuous method, but that a proper PEOc content control was needed to maximize foam expansion. POLYM. ENG. SCI., 51:2387-2397, 2011. (C) 2011 Society of Plastics Engineers