The KFWB series foil strain gauges have the surface covered with a special resin for waterproofing. The waterproof structure enables these gauges to serve for outdoor or underwater measurement merely by being bonded to measuring objects. The insulation resistance shows virtually no deterioration even after 100 hours of use under underwater pressure of approximately 10 MPa. In addition, the covering resin is flexible enough to enable easy bonding to curved surfaces.