To produce iPP products, it is highly possible that the iPP com- pounded with nucleating agent may be subjected to more than one heating process. In the current research, a re-heating was con- ducted on the iPP/b-NA pellets by using a twin screw extruder at the processing conditions described in Section 2.1. As is evident in Fig. 3, the Kb still increased after re-heating but at a slower rate. Re-heating initially reduced the stability of the b-crystals phase in the b-NA nucleated iPP. The Kb of 0.80 was found at the b-NA con- tent of 0.20 wt%, beyond this concentration the Kb seemed nearly constant at a slightly higher level of Kb than those observed in the first heating. The degree of b crystallinity (Xb) was estimated by applying Eq. (4).