Conductivity is defined by the ratio of current per unit area (current density) to the electric field in a material. Conductivity is expressed in units of siemens/metre.

Conductivity can be measured from tapes, films or bars. Surface or volume conductivity – or resistivity – is measured using different kinds of electrodes, depending on which standard test is made. A typical way of evaluating resistivity is with a four-point-electrode-system and with a defined voltage, measuring the voltage drop with the inner electrodes and calculating the resistivity of the sample.