This work investigates the performance of blends in rotational molding, by using an industrially relevant system consisting of polypropylene (PP) and an ultra-low-density ethylene-alpha-olefin copolymer (or polyolefin plastomer, POP). Specifically, the effect of POP content and PP type on the sintering and densification behavior, as well as the rotomolded part properties and morphology, was examined. The sinter-melting curves of these blends exhibited bimodality, due to the wide melting point difference between the two polymers. Increasing POP content resulted in higher sintering and densification rates, as well as improved impact properties and elongation at break, counteracted by lower stiffness. Selection of a polypropylene component with lower viscosity led to better sintering and densification characteristics, due to enhanced flow proper-ties. Better overall performance in terms of mechanical properties was obtained when polypropylene/polyethylene impact copolymers, as opposed to a PP homopolymer, were used. (C) 2004 Society of Plastics Engineers.