Type of Substances - Basis of their resistance:
On the basis of their resistance, substances can be classified as good conductor, semiconductor and bad conductor.
Materials along with low resistance and high conductance are known as the good conductors of electricity.
Metals (like, aluminium, copper, silver etc.), acids and electrolytes.
Materials that are bad conductors at low temperature and good conductors at high temperature are classified as the semiconductors. Such materials are partially conducting, but also have properties of an insulator. The amount of current conduction that may be supported may be varied by "doping" the material with suitable materials, which results in the enhanced presence of free electrons for current flow. They have medium resistance (between good and bad conductors) at room temperature.
Silicon, Germanium, GaAs.
Bad Conductors or Insulators
Materials which offer very high resistance to flow of electricity are termed as the bad conductors of electricity. They are normally utilized as the insulator in electrical machines.
Glass, Mica, Paper, Wood, Rubber ,Bakelite etc.