By analogy with semiconductor technology one speaks of doping the polymer when it is subjected to oxidation with iodine vapour. The more electrons are removed, the higher the degree of doping and the greater the conductivity. While polyacetylene can be persuaded to conduct current as well as many metals do, this material is unfortunately no good for practical use. Its conductivity drops rapidly in contact with air. This has led to the development of more stable, conjugated polymers, e.g. polypyrrol, polyaniline and polytiophene.