Polypropylene (PP) typically produces foams with poor cell morphology and limited expansion due to low melt strength and a lack of strain hardening – causing cell coalescence. Research to improve PP foamability has focused on low-melt flow rate (MFR) resins, whereas methods such as foam injection molding (FIM) require high-MFR resins for easy processability. This thesis evaluates the use of high-MFR, high molecular weight (M_w) PP resins for use in FIM processes. In linear PP, high M_w correlated to higher expansion capabilities due to higher crystallization temperatures and improved extensional rheology. However, low M_w correlated to increased cell nucleation, which is attributed to decreased interfacial tension. Relative to linear counterparts, long-chain branching was found to further increase crystallization temperatures and exhibited strain hardening, resulting in improved high-temperature foaming. These findings provide insights into the mechanisms governing expansion and cell nucleation in high-MFR PP resins, which can guide application-based resin selection.