The thermal behavior of a series of poly(ethylene oxide) (PEO)/stearic acid blends was investigated by means of differential scanning calorimetry (DSC), modulated temperature DSC, Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) for application as thermal energy storage materials. It has been found that PEO/stearic acid blends are efficient polymer-based phase change materials that can be applied in the temperature range 55.7–75.2°C with the enthalpy of phase transition values in the range of 202.8–252.3 J/g. The PEO/stearic acid blend (1:3 w/w) exhibits a senergistic effect—its value of enthalpy of melting and crystallization is higher than those of pure components. The origin of this promising effect was investigated by FT-IR and SEM techniques to ascertain the influence of hydrogen bonds on the sample's supramolecular morphology. Copyright © 2005 John Wiley & Sons, Ltd.