A material which exhibits efficient thermal or electrical transference through itself is said to have a high conductivity. Conductivity in a material is rated as its resistivity, the inverse of conductivity, in ohms per meter. Metals have a high conductivity owing to the large number of free electrons in metal atoms which efficiently transfer the current or heat from one part of the material to another. An insulator, on the other hand, is a material with few free electrons, and hence does not readily pass heat or current.