Conductive plastics:

Plastics are polymers, that is, chains of many identical molecules (monomers) that are intercoupled. The reason that most plastics are isolators is that their electrons are localized. Each electron is firmly fixed, as it were, to its own atomic nucleus. This means that the electrons, carriers of the electric current, cannot move freely in the material. In conductive or semiconductive plastics, discovered by accident in Japan in 1977, this is different. In these, the polymer chains have conjugated connections. This means that the discrete atoms are interconnected alternately by a single and a double chemical bond.