The thermal behaviors of linear and branched polypropylene (PP) with foaming additives were investigated using a normal and a high-pressure differential scanning calorimeter (DSC). Specifically, the effects of material branching, dispersed additives, cooling rates, and dissolved blowing agents on the crystallization temperature of PP resins were elucidated. Introducing branches between polymer chains increased the crystallization temperature of PP significantly. Foaming additives such as talc and glycerol monostearate (GMS) as well as processing parameters such as cooling rate also played major roles during the crystallization process. The experimental results indicate that the crystallization temperature increases up to 30 degrees C by introducing branches and/or adding additives to the PP materials. However, the crystallization temperature was lowered as the supercritical fluid (such as nitrogen or carbon dioxide) was dissolved in the branched PP. The effect of hydraulic pressure was identified by performing DSC study by employing helium as an inert gas, which has a very limited solubility in the polymer matrix.