Many technical applications require using the materials with high thermal stability and thermal conductivity. The tendency of energy and resources saving defines the exploitation of light artificial materials like polymers instead of metals, for example, where it is possible. Such fillers as boron carbide, silicon carbide, boron nitride, aluminum nitride, metal oxides, carbon nanotubes and nanoparticles are used for managing the polymer matrix properties. The effect of interaction between polymer and filler depends on type of matrix, its chemical structure, polymer and filler availability of functional groups, conditions of composite formation and others. The object of the study is low-density polyethylene (LDPE) filled with silicon carbide of different particle’s sizes. Samples were made in Grodno Branch «Research Center of ResourcesSaving Problems» of HMTI. The effect of the filler’s concentration and size on the heat transfer characteristics of composite polymer material was investigated. Silicon carbide is characterized with high thermal conductivity (∼110 W/m⋅K) where LDPE thermal conductivity is ~0.3 W/m⋅K. Certified silicon carbide by Ukraine (black SiC with particles size less than 1 μm and green SiC with particles size 45-63 μm) was used as a filler. Its concentration varied from 0.5 to 60 mass%. Thermoanalytical and thermophysical research methods are successfully used for the determination of phase transitions, destruction, specific heat and thermal conductivity of the composites under interest. Simultaneous TG-DSC analysis was carried out by STA 449 F3 Jupiter (NETZSCH) in the temperature range 25 - 150 °С. Thermophysical properties were determined on the LFA 457 MicroFlash (NETZSCH) by a laser flash method in the temperature range 25 - 90 °C. Experiments were carried out in nitrogen atmosphere. It has been shown that size of SiC particles doesn`t influence on specific heat but this thermal parameter is reduced with filler concentration increase. It is due to limitation of mobility of macromolecules chains of polymer matrix. At the same time, thermal conductivity raises together with filler concentration because of density increase and formation of percolation chains by particles. No any decomposition observed of the composites under investigation in the chosen temperature range. The peculiarities of phase changes of LDPE based composites don`t depend on SiC particles size and even their presence. Temperature of phase changes is almost stable and doesn`t significant affected by SiC concentration or type. But the higher concentration of the filler is, the lower melting enthalpy of polymer composite is. It is explained by weak chemical interaction between LDPE matrix and SiC particles and cause low thermal stability of the composite.