In this study the influence of different fillers on the mechanical properties of physically foamed high density polyethylene (HDPE) were examined. The aim was to determine the effect of cellulose fibre, glass beads and CaCO3 on the processing conditions, mechanical properties of the foam and foam morphology. Therefore, several compounds were prepared with a twin screw extruder using different amounts of the fillers and a fixed amount of a nucleating agent. All compounds were characterized with a cone plate rheometer to compare the influence of the different fillers on the rheological properties. Additionally a scanning electron microscope (SEM) was used to investigate dispersion of the filler and the nucleating agent. The foaming behavior of the compounds was investigated by using a single screw extruder with a screw diameter of 45 mm and supercritical CO2 as foaming agent. For the characterization of the mechanical properties a tensile testing maschine was used. The different compounds were compared in terms of their influence on the processing conditions, mechanical properties and foam morphology.