The thermal conductivity and the cellular structure as well as the matrix polymer morphology of a collection of chemically crosslinked low-density closed cell polyolefin foams, manufactured by a high-pressure nitrogen gas solution process, have been studied. With the aid of a useful theoretical model, the relative contribution of each heat-transfer mechanism (conduction through the gas and solid phases and thermal radiation) has been evaluated. The thermal radiation can be calculated by using a theoretical model, which takes into account the dependence of this heat-transfer mechanism with cell size, foam thickness, chemical composition, and matrix polymer morphology. A simple equation, which can be used to predict the thermal conductivity of a given material, is presented. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 993–1004, 2000