This paper presents an experimental study on the mold design and the effect of processing parameters on the expansion of foam injection molded parts. Limitation in foam expansion is a primary challenge in foam injection molding process. In this study a novel approach in mold design is introduced to take advantages of concepts such as counter-pressure and mold opening to further extend the expansion range. A modular sheet mold with a rectangular cavity and a fan gate was designed and manufactured. The mold includes a main cavity, the thickness of which could be varied, connected to an overflow channel via a secondary gate, the size of which was also varied in this research. The investigated parameters were part thickness, secondary gate width. Full factorial test experiments were carried out in this research work. The results indicated the high effectiveness of the proposed approach in further reducing the foamed part weight. For the parts with a larger thickness, a noticeable decrease in bulk density and an increase in cell population density along with an improvement in cellular structure uniformity were observed.