The thermal conductivity, the cellular structure and the matrix polymer morphology of a collection of chemically crosslinked low-density closed cell polyethylene foams, manufactured by a high-pressure nitrogen gas solution process, have been studied. With the aid of theoretical models, the relative contributions of each heat transfer mechanism to the total thermal conductivity has been evaluated. The results show that, the relative contribution of the thermal radiation is (22-34%), and that this contribution is mainly controlled by the mean cell size and by the carbon black content in the foam.