The history of plastics over the last half century has been as a replacement for metal. For structural applications, plastics have made tremendous headway, but not where electrical conductivity is required because plastics are good electrical insulators. This deficiency is overcome by loading plastics up with conductive fillers, such as carbon black and graphite fibers (the larger ones used to make golf clubs and tennis racquets). The loading required to provide the necessary electrical conductivity is typically high, resulting in plastic parts whose structural properties are degraded. Carbon nanotubes blend well with plastics, and can impart reasonable conductivity at modest loadings.
It is well established that the higher aspect ratio of a filler, the lower loading required to achieve a given level of conductivity. Carbon nanotubes are ideal in this sense, since they have the greatest aspect ratio of any carbon fiber. In addition, their natural tendency to form ropes provides inherently very long conductive pathways even at relatively low loadings. The image above shows carbon nanotubes well dispersed in polycarbonate. This composite is highly electrically conductive. If this plastic is formed into an enclosure for sensitive electronics, it protects the internal circuitry from radiofrequency interference outside the enclosure, and it keeps any radiofrequency interference from escaping from within the enclosure.