In the present work, we study the thermal behavior of Polymer (Polystyrene) dispersed (4-cyano-4'-pentylbiphenyl) 5CB liquid crystal film composite. A photopyroelectric device was used to study thermal conductivity at homeotropic and planar aligned of 4-cyano-4'-pentylbiphenyl (5CB) liquid crystal. Thermal conductivity of polystyrene (PS) has been determined and calculated from experimental applied data reported in the literature. Thermal conductivity characteristics of the PDLC films were investigated with three prediction models as a function of both temperature and liquid crystal concentration in the polymer matrix. We particularly show the behavior of this thermal conductivity in the ON and OFF state. It was found that the difference in the film thermal conductivity ranges between 3 and 21%, depending on the ON and OFF state and the liquid crystal volume concentration. (C) 2003 Wiley Periodicals, Inc.