Corn. starch was compounded with powdered pine bark (up to 30% by mass), plasticized with glycerol (20% by mass), granulated by extrusion at 80-120 degrees C (screw speed 60-100 rpm) and finally studied for thermal behavior in air. Three-stage decompn. was obsd. Up to 473 K, weak chem. bonds were destroyed only. Up to 673K, the composite material was oxidized. At higher temps., the combustion of org. matter and C took place. Decompn. rate constants, reaction orders, activation energies and pre-exponential factors were calcd. from the exptl. data. The addn. of fibers resulted in a decrease in thermal resistance of the composite material.