This paper presents plastic foam processing for the manufacture of LLDPE foams in rotomolding. In order to better understand the mechanisms of foaming, a fundamental study on the foaming process in rotomolding has been conducted. First, the decomposition behavior of the chemical blowing agents was studied by a thermogravimetric analyzer (TGA). The rheological properties of zero-shear viscosity and melt elasticity for LLDPEs were measured using a rotational stress rheometer. Also, an optical microscope with a hot stage was effectively used to study the cell nucleation, growth, coalescence and coarsening in LLDPE melts which provide an improved understanding of the foaming dynamics with a chemical blowing agent in rotational molding. Finally, the actual foaming behavior in rotomolding has also been studied. The experimental results indicate that the amount of blowing agent, the heating time, and the processing temperature play an important role in determining the cell morphology in rotational foam molding.