In this study, form-stable phase change material (PCM)-high density polyethylene (HDPE)/paraffin hybrid with different flame-retardant systems are prepared by using twin-screw extruder technique. This kind of formstable PCM is made up of paraffin (a dispersed phase change material) and a HDPE (a supporting material). Their structures and flammability properties are characterized by scanning electronic microscope (SEM) and cone calorimetry. Thermal stability is shown by thermogravimetry analysis (TGA) and its latent heat is given by differential scanning calorimeter (DSC) method. SEM results show that the HDPE forms a three-dimensional net structure and the paraffin is dispersed in it. The peak of heat release rate (HRR) of the flame-retardant form-stable PCM decreases markedly. In TGA curves, although the onset of weight loss of flame-retardant form-stable PCMs occur at a lower temperature than that of form-stable PCM, flame-retardant form-stable PCMs produce a large amount of char residue at 700 degrees C. DSC results show that the addition of flame retardant has little effect on the phase change latent heat of PCM. (c) 2005 Wiley Periodicals, Inc.