New ethylene-co-vinyl acetate (EVA, with 60% vinyl acetate content) based nanocomposites were prepared with graphites modified by various techniques and a commercially available expanded graphite (EG). The infrared spectra and the surface energy measurements indicated better oxidation and higher surface energy of the graphite modified by mixed acids followed by high temperature treatment (GO). Interlayer space and surface area were increased as a result. EG possessed higher surface area. GO was found to distribute in finer tactoids of average thickness of 25 nm in the matrix, as compared with the unmodified graphite (UG), having average tactoid thickness more than 40 nm along with aggregation. EG also showed finer dispersion in the EVA matrix with some network formation. The dynamic mechanical and the mechanical properties were superior at the 2 wt% concentration of the GO, beyond which the improvement was less, possibly because of aggregation of GO. Greater EVA-GO interaction at 2 wt% concentration was also supported from the swelling analysis, thermal conductivity, and the thermo-oxidative degradation data of the hybrid composites. The melt viscosity was lower at 2 wt% GO concentration. EG based nanocomposites registered similar properties. (c) 2008 Wiley Periodicals, Inc.