The non-isothermal and isothermal crystallization of different types of commercial polypropylenes (PP) are investigated by fast scanning calorimetry and wide-angle X-ray scattering. Typically, PP shows two different crystallization processes: below 55 degrees C the mesophase formation and at higher temperatures the alpha-phase formation. Here we report the first observation of an additional crystallization process in some PP-types. It is observed between 45 degrees C and 75 degrees C, and is understood as a consequence of an additional nucleation of alpha-phase crystals. (C) 2015 Elsevier B.V. All rights reserved.