The surface resistivity provides information on the level of insulation on the surface of the insulating material (sample specimen), which depends on humidity and surface contaminations. According to DIN 53482, spring metal blade electrodes with a length of 100 mm are positioned on a plane sample at a distance of 10 mm or bar electrodes with a length of 25 mm and a width of 1.5 mm are positioned at a distance of 2 mm. According to DIN and in contrast to ASTM standard D 257 no surface resistivity is specified. The resistance is determined at 1,000 V DC by means of current-voltage measurement. During every measurement of the surface resistivity, part of the current (between the electrodes on a surface) is distributed through the volume of the material. Hence, if the resistivity of the surface area is not lower than that of the inside or if this area is sufficiently thin, the surface resistivity is mostly a function of the volume resistivity and the surface resistivity itself is of minor importance.
