Results of experimental investigation and estimates of the contributions of the phonon, diffusion, and photoncomponents of thermal conductivity of polyvinylchloride and poly (vinyl butyral) in the range 290 K ≤ T ≤ T v + 40 K have been presented. It has been shown that the phonon mechanism of heat transfer predominates at 293 K ≤ T < T v , and the diffusion mechanism, when T ≥ T v . The value of the photon component of thermal conductivity nonlinearly decreases throughout the T range.Introduction. The quantitative characteristic of the efficiency of the process of transfer of thermal energy from a more heated part of a body to a less heated part is its thermal-conductivity coefficient λ.Pioneering works on investigation of λ of dielectrics, among which are most of the organic polymers, belong to P. Debye, R. Peierls, K. Eierman, P. Klemens, et al. The history and works on this issue up to 1978 have been reviewed by I. I. Perepechko in [1] and up to 1982, by Yu. K. Godovskii in [2], where it has been indicated that most of the carried-out investigations sought to establish the dependence of λ on the structure, the chemical composition, and the temperature of condensed media. For amorphous polymers, the most developed is the Eierman model [3]; however, it has a number of substantial drawbacks [4] and is inapplicable to systems with a complex structure. Since heat conduction in its physical meaning characterizes the capability of a body for transferring thermal energy through the interaction of atoms, atomic groups, and parts of macromolecules [5], the value of λ is largely determined by the intensity and character of intra-and intermolecular interaction. Theories concerning the heat conduction of polymers use the model approach characteristic of liquids [6] and/or the scattering of phonons, which are considered as heat carriers only conventionally [7]. In this case phonons as carriers of thermal energy of a body [8] interact with each other via nonlinear properties of a medium [9]. This leads to an energy redistribution between shear and longitudinal vibrations of structural elements, whereas the macroscopic flow of kinetic energy appears as the heat flux [10]. One recognizes [11] three characteristics of thermal motion in polymers: fast relaxation processes -motion of parts of a macromolecule, side chains, or individual atomic groups, sharp increase in segmental mobility (principal relaxation region), and viscous-friction background [12]. It has been proved [13] that the entire spectrum of interchain vibrations can be represented by one parameter, i.e., the characteristic temperature of a body θ. Klemens [7] has assumed that the major contribution to the low-temperature thermal conductivity is made by longitudinal waves (longitudinal phonons). The process of transformation of longitudinal waves into transverse waves limits the mean free path of a phonon, which affects the character of the dependence λ = f(T) [1]. However, this brings up a number of unsolved problems associated with the introduction and selection ...