Conductivity is a measure of a material’s ability to conduct an electric current. It is commonly expressed as a percentage of the International Annealed Copper Standard (IACS). The IACS value for pure copper at 20°C is 100%, so the conductivity of a material that has IACS = 50% would be half that of pure copper.
The vast majority of electrical and electronic applications make use of materials that are very good conductors, such as metals. However, there are also many important applications for materials with much lower conductivity, such as semiconductors.
The electrical resistivity of a material is the reciprocal of its electrical conductivity. It measures a material’s resistance to the flow of an electric current. The SI unit for electrical resistivity is the ohm-metre (Ω⋅m).