An electric humidity sensor element often used in radiosonde equipment that relies on changes in the resistance of a humidity-sensitive component. A carbon humidity element is used in the United States. It comprises a polystyrene slide or strip with two metal electrodes along the long edges sprayed with a mixture of carbon particles and a cellulose binder. The binder changes its volume with relative humidity in such a way that it separates the carbon particles from each other as the humidity increases, thus increasing the resistance between the electrodes. The relative humidity is calibrated as a function of resistance.