In recent years, many parts of the automotive industry, previously made of metal, has been passed to polymers due to their light weight, ie lower carbon emission and fuel consumption advantage. The aim of this work was to investigate the microstructure and mechanical properties of chemical foaming agent added polypropylene foam samples produced by injection molding. In particular, the effects of injection speed and core back distance on the evolution of cell diameter, compact outer layer thickness, cell density and mechanical properties were examined. In the first step the effect of various injection speeds (110; 125; 140 mm/s) was investigated. Then, various core back positions (0; 0.7 and 1.5 mm) were analyzed at a constant injection speed (110 mm/s). The results showed an increase of the cell diameter, the compact outer layer thickness and the elastic modulus as the injection speed increases. In addition, an important effect of the core back distance was observed with the presence of a critical core back distance. Below this critical value, the cell diameter and the elastic modulus drop due to a notable decrease of the skin layer thickness. Above this critical value, the cells started to collapse and lose their circularity.