We previously developed a resilient and innovative cellular foam injection molding (RIC-FIM) technology to illustrate that pressurization of the physical blowing agent (PBA), such as carbon dioxide (CO2), to the supercritical state is unnecessary for preparing microcellular foams. Herein, our developed FIM machine is further simplified by using the previously auxiliary venting unit as the only PBA delivery unit. Subsequently, high void fraction polypropylene (PP) foams were successfully obtained using this novel FIM machine with 4-6 MPa of nitrogen (N-2). The results showed that an increase in the vessel pressure reduced the PP foam cell size and enhanced the cell density as well as the void fraction, signifying that the concentration of dissolved gas was controlled by the pressure vessel. Furthermore, compared with the N-2 foaming process, CO, foaming revealed a finer cellular structure for PP. This simplified FIM technology holds great potential for the industrial manufacturing of lightweight injection-molded products with better economic benefits.