Almost all materials reflect ultrasonic energy and can be detected. Ultrasonic energy, striking a flat, hard, smooth surface, perpendicular to the transmitted sonic beam, is the ideal condition for reliable detection.

Conversely, materials with coarse, textured surfaces diffuse or absorb much of the transmitted energy. For example, granular products, foam rubber materials and certain textiles and papers may need a stronger transmitted signal for reliable detection. Detection of foam surfaces from soaps and similar products is also difficult and should be tested prior to installation.