We carried out a systematic study of the electrical properties of carbon nanotube-based polymeric composite materials. Our purpose was the production and characterization of a light, thin and mechanically strong new composite material able to cover electric circuits against external electromagnetic interference. As polymeric matrix we used a commercial Shell product Epon 828 epoxy resin. Two types of curing agent were used along with the resin, namely A1 and PAP8 agent: the composite was obtained using the A1 curing agent, selected for the stability of the corresponding material over a wide range of pressure values. Setting the resistivity properties of carbon nanotube-based composites against those containing micro-sized graphite particles as constituent we showed the advantages of using carbon nanotubes. The change in the resistivity values for carbon nanotubes-based composites turned out to be significant, even for small changes in the added carbon nanotubes percentage. We also plan to show the composite's behavior in controlled humidity environments and for different temperatures. These results might be important for determining the most suitable "recipe" for the realization of composite materials useful to high-fidelity circuits applications, or even in devices exposed to predominantly electromagnetic noise.