Fillers and additives can be classified into inactive nucleating agents, that have no significant influence on the crystallization kinetics, and active nucleating agents, that accelerate the crystallization process. The active nucleating agents can be further classified in particulate additives and additives which self-assembly the structure which accelerates crystallization On the example of polypropylene (PP) the nucleating activity is measured in a wide temperature range (between 0 °C and 130 °C) using Fast Differential Scanning Calorimetry (FDSC), the recently introduced Flash DSC 2+. The influence of sorbitol-type nucleating agents, different carbon-nanotubes, calcium carbonate and nano-diamonds of the isothermal and non-isothermal crystallization kinetics is analyzed. As a result it could be shown that all additives of investigation influences the crystallization process of PP. Furthermore it is shown, that all additives (also calcium carbonate) accelerates the crystallization process in a dedicated temperature range. Outside of this range the nucleating agents are not active. The measurements have been shown further that especially the measurement of the isothermal crystallization process is very sensitive for the characterization of the nucleating activity of an additive.