Electrical conductivity is the ability of a material to transmit current or the movement of charged particles, most often protons. Materials that carry the flow of electrical current are called conductors. Metals, such as silver and aluminum, are some of the best conductors of electricity. Other good conductors of electricity are copper and gold. Materials that do not permit the flow of electrical current are called nonconductors or insulators. Wood, paper, and most plastics are examples of insulators. Resistance is defined as the extent to which a material prevents the flow of electricity. Materials with a low resistance have a high conductivity while those with a high resistance have a low conductivity. German physicist Georg Simon Ohm (1789–1854) was the first to describe the laws of electrical conductivity and resistance.