The goal of this research is to develop a scientific and engineering basis needed for production of thermoplastic foams in rotomolding using a chemical blowing agent (CBA). Both polyethylene (PE) and polypropylene (PP) were used for the foaming process, but a special emphasis was given to PP, due to its many advantages. Two types of methods were utilized in the research, namely the dry blending method and the melt compounding method. Decomposition behaviors of different CBAs were analyzed with a Thermogravimetric Analyzer (TGA) and a Differential Scanning Calorimeter (DSC). The zero-shear viscosities of polymers that determine the sintering behavior of plastic powder particles were studied with a rotational rheometer. The mechanisms that govern the cell nucleation, sintering, and cell distribution for both the dry blending and the melt compounding methods were clarified. The critical processing parameters that govern the mixing, foaming and skin formation were outlined. Based on these investigations, conclusions were drawn on the selection of polymer material, application of CBA, and the determination of processing conditions.