The main aim of this work was examinations of polymer shearing conditions during structural foam injection moulding and their influence on structure and properties of moulded parts. The mulded parts from polypropylene (Malen P J-400) containing exothermic chemical blowing agent (Adcol-blow UP-0EB-X1099) were examinated. The effect of the blowing agent content and the level of holding pressure on structure and shrinkage of moulded parts injected to the cavities of variable height was determined. In experimental examinations parts thickness was examinated, and also as indicator of the parts quality: luminance and gloss were investigated. Morphological examinations of parts were also conducted. The most intensive foaming process was observed in the part of the cavity of the biggest thickness (4 mm).