Novel polyethylene- and polypropylene-based electromagnetic wave shielding and absorbing composite materials with low combustibility, enhanced thermal and mechanical properties, containing graphite, grinded wood, and fire retardants, were developed and investigated. Flame-resistance, thermal and mechanical properties of these materials was investigated. Electromagnetic wave reflection coefficients over the frequency range 20-40 GHz were measured; at moderate concentration (10-15%) of functional filler, reflection coefficient can be as low as -16 dB for PE and -11 dB for PP composite, respectively. Coke formation mechanism was investigated, the principal role in this process is attributed to aromatization and condensation of aromatic compounds with the formation of polycyclic aromatic systems, an important role of phosphoric acids in accelerating this process was found. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 2775-2782, 2010