In this study, polypropylene (PP) foams were prepared with 1.0 wt% of cucurbituril (Q), zinc acetate (Zn(Ac) 2 ), Zn@Q (a supramolecular compound synthesized from Q and Zn(Ac) 2 ), or a mixture of Zn(Ac) 2 and Q (weight ratio of 1:1) through injection molding in the presence of a chemical blowing agent, azodicarbonamide. The effect of the additions on the crystallization behavior and foaming performance of PP and the mechanical characterizations of the foaming samples were determined. The results showed that the additions can change the crystallization type from homogeneous to heterogeneous, increase the crystallization rate and shrink the size but increase the density of spherulites. Among the additions, Q most significantly altered the crystallization properties. Scanning electron microscopy (SEM) images revealed that the PP foaming performance can be improved by Zn(Ac) 2 addition at a lower temperature (175°C); however, further increasing the temperature had an undesirable effect. Q exhibited the optimum foaming improvement effect on PP in a wide temperature range (175–195°C). Adding nanoparticles also enhanced the tensile properties, flexural strength and impact strength of foaming PP at low temperatures. However, with increasing temperature, the poor cell structure demonstrated undesirable effects in terms of tensile strength, flexural strength and impact strength.