Abstract: An adaptor for supporting small thin film or fibrous samples of material between the electrodes of a resistivity cell is described which comprises a pair of stacked electrically insulating plates, each plate having a central electrode therethrough and presenting confronting conductive surfaces of known surface area for sandwiching the sample therebetween for resistivity measurement, and a guarding electrode on one confronting plate surface and surrounding the central electrode thereon for electrically contacting the guarding electrode of the resistivity cell; the plates may be hingedly joined along respective sides and include fittings to maintain the confronting electrode surfaces in concentric alignment with the sample therebetween.