Sonite is a material used for acoustic decoupling in deep‐ocean sonar transducers. Its density, bulk modulus, sound velocity, and attenuation constant have been measured as a function of precompression and ambient pressure. The sound velocity and attenuation constant were measured at 40 kHz and 12°C, utilizing a water‐filled impedance tube. By using a delay line technique at 1 MHz, the material was found to exhibit transverse isotropy. Sample preparation and measurement techniques are described.