Materials that allow electrons to flow through them easily are called electrical conductors. In all metals, outermost electrons in each atom are so loosely held that they are able to move freely between atoms. These free electrons make metals very good electrical conductors. Non-metals, such as graphite and some solutions are also good conductors.
- Conductors can be discharged through a process known as earthing.
- Earthing allows electrons to flow into (in the case of a positively charged object) and out of (in the case of a negatively charged object) the object.
Materials which do not conduct charges are called non-conductors or insulators. Their electrons are all tightly held to atoms and are not normally free to move- though they can be disturbed if a material is rubbed. Examples of insulators include rubber, glass, diamond, most plastics, dry wood and dry air.
- Insulators can be discharged by heating or providing humid conditions.
Insulators have very few free electrons (about 1 per cubic millimetre, for plastics). Conductors have many free electrons (about 1 billion per cubic millimetre, for copper).