A capacitive vapor sensor, sensor system, and method for determining a vapor concentration is provided. The capacitive sensor includes a first electrode and a second electrode. The first and second electrodes are configured to provide a bias voltage. The sensor further includes a cantilevered sensor electrode interdigitated between the first and second electrodes and having an adsorptive polymer attached to a surface of the cantilevered sensor electrode. The adsorptive polymer is configured to expand in response to adsorbing a vapor and cause a deflection of the cantilevered sensor electrode, the deflection causing a change in a differential capacitance of the first and second electrodes. A sensor indicates current at the cantilevered sensor electrode, and an electronic processor determines the change in the differential capacitance to determine a characteristic or concentration of the vapor.