Abstract The present study reveals that the observed variation of thermal conductivity λ with temperature, for any non-conducting linear amorphous polymer can be explained by considering phonons as chief heat carriers. It is proposed that in the temperature region below the glass transition temperature, T g, structure scattering and chain-defect scattering are the predominant phonon scattering processes, while above T g, vacant-site scatterings also play a significant role. Owing to the effect of temperature on the movement of structural units, the thermal resistances corresponding to these scattering processes have temperature dependence. Accordingly, relations for λ can be deduced using Matthiessen's rule. Calculated values of poly(vinyl chloride) with 0%, 10%, 20% and 40% plasticizers and several different styrene polymers are in excellent agreement with the reported experimental data, over a wide range of temperatures around T g, maximum deviations being ∼ 3%.