Rotational moulding is a processing method used to produce hollow objects by loading a thermoplastic powder into a mould that is simultaneously rotated into two principal axes. Many rotomoulding applications use polymer powders with irregular surfaces, requiring nonspherical particle models to understand the process. In this chapter we present one of those models, looking in particular at the use of natural fibre reinforced thermoplastics (NFRP). The melt densification process of polyethylene powders filled with natural fibres is analysed to understand the underlying principles that take place in the consolidation of polymer-fibre systems processed by rotational moulding. These results can be used to assess the efficiency of reinforcements or as a quality control tool for rotomoulded products. Nanocomposite polymeric materials processed by rotational moulding are briefly discussed at the end of the chapter. Some comments on recent work on the use of biobased polymers, such as thermoplastic starch, in rotational moulding are also provided. © 2009 Woodhead Publishing Limited.