Small amount of N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide as a beta-form nucleating agent is dissolved beyond 280 degrees C in a molten isotactic polypropylene (iPP) and appears as needle crystals around at 240 degrees C during cooling procedure. Further, iPP molecules crystallize on the surface of the needle crystals, in which c-axis of the beta-form iPP crystals grows perpendicular to the long axis of the needle crystals. Under flow field at extrusion processing, the needle crystals orient to the flow direction prior to the crystallization of iPP. As a result, c-axis of the beta-form iPP crystals orients perpendicular to the applied flow direction with a small amount of alpha-form iPP. Moreover, the vertical molecular orientation of the extruded sheet sample is responsible for unique mechanical anisotropy; the fracture occurs along the transversal direction. (C) 2009 Elsevier Ltd. All rights reserved.