For the purpose of improving the thermal conductivity of the form-stable phase change materials (FSPCM), two types of nano-powders with high thermal conductivity were added into the samples. In the modified FSPCM, myristic acid (MA) was used as a solid-liquid phase change material (PCM), high density polyethylene (HDPE) acted as supporting material to prevent the leakage of the melted MA. Nano-Al2O3 (NAO) and nano-graphite (NG) were the additives for thermal conductivity enhancement. Scanning electronic microscope (SEM), Fourier transformation infrared spectroscope (FT-IR) and X-ray diffractometer (XRD) were used to analyze the microstructure, chemical structure and crystalline phase of the samples, respectively. Furthermore, the specific latent heat and phase transition temperature, thermal conductivity and thermal reliability were investigated using differential scanning calorimeter (DSC), thermal conductivity meter and thermo-gravimetric analyzer (TGA). The results showed that the MA was uniformly absorbed in the HDPE matrices and there was no leakage during the melting process when the mass fraction of the MA in the MA/HDPE composite was less than 70%. The DSC results revealed that the modified FSPCM have a constant phase change temperature and high specific latent heat. The thermal conductivity of the FSPCM was measured in the solid (30 degrees C) and liquid (60 degrees C) states of the MA. When the mass fraction of nano-powder additives is 12%, the thermal conductivities of the FSPCM increase by 95% (NAO) and 121% (NG) at 30 degrees C. It is anticipated that the FSPCM possess a potential application for thermal energy storage. (C) 2016 Elsevier Ltd. All rights reserved: