Abstract: A vapor pressure sensor comprising a substrate having a body with first and second planar parallel surfaces. A hole is formed in the body and extends through and between the first and second surfaces. A beam is disposed in the hole in the body and is formed integral with the body and forms a junction with body and is formed as a cantilever in the hole in the body. The beam has a surface. A vapor adsorbing coating is carried by the surface of the beam and the coating is substantially uniform in thickness. It is adhered to the surface of the beam and is fully shear restrained by the beam. A strain measuring device is carried by the substrate and disposed at the junction between the body and the beam to measure shear forces placed in the beam by the vapor adsorbing coating. The vapor adsorbing coating expands and contracts in directions parallel to the surface of the beam as the vapor adsorbing coating adsorbs and desorbs vapor.