Injection foam molding provides the industry with advantages from production through to the life cycle of plastic components. Despite numerous applications, many questions regarding the fundamentals of this technology are fraught with uncertainty. One aspect of supreme importance is the relationship between the gas content during processing and its influence on process and part performance. In order to refine the foaming technology and to comply with modern market requirements it is crucial to understand this dependence as proper process design and tailoring of mechanical properties requires this knowledge. This work represents a thorough investigation of the influence of CO2 content on both the process and the produced components. Using talcum filled polypropylene in a MuCell® process initially the dynamic solubility limit, i.e. the ultimate amount of gas dispersible in the polymer melt during an injection molding process, was determined via a bulk modulus methodology. During this procedure, foamed plates were molded at different CO2 contents. Processing parameters, morphology and bending behavior of the produced plates were monitored and measured. The results show interesting mechanical behavior, especially close to the determined solubility limit. Based on these outcomes our experiments clearly argue for larger gas contents in physical foaming, which also benefit injection pressure/work or torque during processing. In contrast to these findings, trials with a chemical blowing agent (also yielding CO2) were carried out with the same material. The TGA of the blowing agent yielded an astonishing difference regarding gas concentration in the melt of one order of magnitude compared to physical foaming. In spite of the vanishingly small amounts of gas in chemical foaming a fine morphology developed. This study provides novel insights into the complexity of injection foam molding, critically assesses gas contents during processing but also poses new questions.