Testing pure resins or resin-fiberglass composites is generally simple and only requires placing the material on the sensor. With carbon-fiber composites, however, a conductive fiber contacting the sensor will short circuit its electrodes and cause bad, unusable measurements. Despite this problem, cure monitoring of carbon fiber reinforced prepreg (CFRP), carbon fiber sheet molding compound (CF-SMC) and similar composites is possible with filtered or coated sensors.