Polymers and plastics are necessarily electrical insulators.

Most everyday plastics are excellent electrical insulators. That is why polymer coatings are so useful around wires and electronic components.

The reason lies in their electronic structure. In many ordinary polymers, electrons are tightly localized in particular chemical bonds and cannot move easily through the material.

For a long time, that made electrical insulation seem like a basic property of polymers as a whole.

Conjugated polymers provided an exception.

In these molecules, the backbone contains a connected pattern of alternating bonds. Their electrons can become spread out, or delocalized, over a larger part of the chain rather than remaining confined to one bond.

That still does not automatically make the material highly conductive. A major change comes from chemical doping. Here, “doping” means adding chemicals that remove or supply electrons, creating mobile charge carriers that can travel through the polymer.

In the late 1970s, Hideki Shirakawa, Alan MacDiarmid, and Alan Heeger showed that doping polyacetylene could increase its electrical conductivity by many orders of magnitude.

Conducting and semiconducting polymers later became useful in sensors, displays, organic electronics, coatings, and energy technologies.

Most polymers remain good insulators. The correction is narrower: being a polymer does not automatically mean being unable to conduct electricity.