Conductors, insulators, semiconductors and wiring
Insulators are materials that do not allow a steady electric current to ﬂ ow through them and they are therefore used to prevent such a ﬂ ow. Most of the insulators that we use are solid materials that are not metals. Natural insulators, such as sulphur and pitch, are no longer used, and plastic materials such as polystyrene and polythene have taken their place. Pure water is an insulator, but any trace of impurity will allow water to conduct some current, so that this provides one way of measuring water purity.