The electromagnetic interference shielding characteristics of polypropylene (PP) and poly(ether imide) (PEI) filled with synthetic graphite composites were studied. The thermal properties were characterized by differential scanning calorimetry and thermogravimetric analysis, whereas the morphologies of the composites were studied by scanning electron microscopy. The viscosity measurements were studied by advance rheometry. The measurements of shielding effectiveness (SE) were carried out in the frequency range 8-12 GHz (X-band range). The return loss and loss due to absorption were also measured as a function of frequency in the X-band range. It was observed that the SE of the composites was frequency dependent, and it increased with increasing frequency. The SE also increased with increasing filler loading. The PEI-based composites showed a higher SE compared to that of the PP-based composites. The correlation between SE and the conductivity of the various composites is also discussed. (c) 2008 Wiley Periodicals, Inc.