A sensor is disclosed for sensing a physical property of a sheet material. The sensor includes a mechanism for supporting one side of the sheet along the periphery of a defined region and a mechanism for forcibly deflecting the sheet into the unsupported center of the defined region. A transducer may also be incorporated to sense the force required to deflect the sheet into the unsupported region and/or the distance that the sheet is deflected into the unsupported region. The sensor may be operatively coupled to a computer programmed to determine a physical property of the sheet based upon the sensed force and/or distance, such as the sheet failure strength.