Abstract: Ultrasonic calibration material produced by polymerization of acrylamide with N,N'-methylene-bis-acrylamide in vacuum-degassed liquid solutions such as water, ethylene glycol, emulsions of non-miscible liquids with water and blends of liquids in which a homogeneous and permanent suspension of solid and liquid particles (e.g.: alumina, boron nitride, graphite, water-filled phenolic microspheres, glass microspheres, polyethylene, turpentine oil) is chemically achieved by polymerization of an acrylic acid polymer.