SJ'nopsiSThe thermal conductivities of linear high polymers were studied experimentally and theoret.ically. A theory of thermal conductivity in linear amorphous high polymers waa derived based on a simple model of molecular structure. Predictions on the effects of molecular weight and molecular orientation on thermal conductivity taken from the theory agree with available experimental data. New data on the thermal conductivity of linear polyethylene and some polyethylene-wax blends are presented. Temperature dependence of the thermal conductivity in polyethylene was analyzed by the per cent crystallinity concept to obtain results which are in accord with the phonon theory of thermal conductivity in dielectric crystals.