Non-conductors are materials in which the atomic structure has no free electrons. They have little or no conductivity.
All electrons of the valence bands are firmly connected with electrons of other atoms and are not available for current transport. Accordingly, the band gap between the valence and conduction bands is very large. It is over 3 eV and can only be overcome with a large amount of energy. Since non-conductors cannot transport current, they are used as dielectric for insulation.
Non-conductors include many inorganic materials such as plastic materials, but also rubber, stone, ceramics, glass and quartz, as well as liquids such as distilled water or oil. The resistivity (`rho`) of non-conductors is between `10^3` and `10^12`.