A model for heterogeneous nucleation of isotactic polypropylene in terms of a "cylindrical cap" with the critical size and barrier set by a contact angle is described. Quiescent crystallization data for bulk samples of isotactic polypropylene are analyzed to extract a contact angle in the range of 40 to 70 with a mean value of 56, which corresponds to a factor of 6 decrease in the critical barrier from the homogeneous case. This value is in reasonable agreement with the contact angle of 79 degrees +/- 3 degrees estimated from molecular scale theory (DOI 10.1021/ma400703m). This model could be combined with calculations from melt rheology of entropy reduction due to flow to frame discussions of flow-induced crystallization.