The resistivities of various common materials are listed in Table. Materials are classified as conductors, semiconductors and insulators depending on their resistivities, in an increasing order of their values.
Metals have low resistivities in the range of 10–8 Ωm to 10–6 Ωm.
At the other end are insulators like ceramic, rubber and plastics having resistivities 1018 times greater than metals or more.
In between the two are the semiconductors. These, however, have resistivities characteristically decreasing with a rise in temperature.
The resistivities of semiconductors are also affected by presence of small amount of impurities.