- A measure of the inherent ability of a material to resist the flow of current. It is the reciprocal of electrical conductivity, and depending on their resistivities, materials can be classified as insulators, semiconductors, or conductors. The lower the specific resistance, the better conductor a material is. Its formula is: r = RA/L, where r is resistivity in ohm-meters, R is the resistance in ohms, A is the cross-sectional area of the material in square meters, and L is its length in meters. Also called resistivity, or electric resistivity.