A rayl[1][2][3][4] (symbol Rayl[5][6]) is one of two units of specific acoustic impedance and characteristic acoustic impedance; one an MKS unit, and the other a CGS unit. These have the same dimensions as momentum per volume.
The units are named after John William Strutt, 3rd Baron Rayleigh.[7] They are not to be confused with the unit of photon flux, the rayleigh.