The thermal diffusivities of 25 kinds of polyolefin films, including high-density polyethylene, low-density polyethylene, linear low-density polyethylene, polypropylene, 4-methylpentene, and ethylene-octene copolymer, were determined by temperature wave analysis in a continuous temperature scan. The thermal diffusivity decreased with increasing temperature, and the temperature dependence was steeper in the solid state than in the melt state. A supercooling phenomenon was observed in the crystallization process during cooling. The thermal diffusivity of polyethylene in the solid state was in a good correlation with the density at room temperature, and a higher temperature coefficient was observed in high-density polyethylene with a higher thermal diffusivity. The influence of the catalyst system on the thermal diffusivity was also observed in the ethylene-octene copolymer. The thermal diffusivity was sensitive to the precise change in the microstructure of the crystalline polyolefin, which was influenced not only by the chemical structure but also by the thermal history. (c) 2005 Wiley Periodicals, lnc.