The crystallization behavior of a commercial chain-extended PET (foam grade) was evaluated and compared to that of bottle-grade PET. Cold and melt isothermal crystallization were analyzed by using the Avrami model. The foam grade PET showed a slower crystallization kinetic compared to the bottle-grade PET. The Hoffman-Lauritzen analysis showed that the energetic barriers to nucleation and molecular mobility were higher for the chain-extended PET. This resulted in a lower nucleation rate in both cold and melt crystallization. (c) 2005 Wiley Periodicals, Inc.