In order to efficiently recover waste heat in the form of latent heat, we studied the impregnation of a porous material with a phase change material (PCM); erythritol was selected as the PCM and expanded perlite (EP), diatom earth (DE), and gamma-alumina (CA) were selected as porous materials. Effects of vacuum in impregnation, pore size of porous materials, holding time and cyclic test on thermal properties of composites; latent heat, melting temperature, were mainly examined by using DSC. The following results were obtained. (1) The pores of EP were completely filled with liquid erythritol by the vacuum impregnation treatment, and the latent heat of the EP/erythritol composite reached 83% of the theoretical latent heat of pure erythritol (294.4 J g(-1)). (2) Porous materials with small pore sizes showed a low melting temperature for phase change composites. (3) The pores of EP were completely filled with erythritol at 1.8 ks immersion in the vacuum impregnation treatment. (4) EP/erythritol composite retained 75% of the impregnated PCM, even in a cyclic process of heating and cooling. In conclusion, the impregnation of porous material with erythritol is a promising method for conserving latent heat with high thermal storage density. (C) 2009 Elsevier B.V. All rights reserved.