By an extension of the techniques of Lindsay, the reflection from a semi‐infinite attenuating medium is derived for the case of oblique angles of incidence. The results are applied to the design of a water tank each wall of which is assumed to be covered by a sheet of absorbing material. The optimum physical properties of the absorber required to make the tank anechoic in the mesacycle region are then determined theoretically. Experimental measurements at 3.35 megacycles/sec indicate that the properties of tanrho‐crubber are very close to optimum. With a14‐inchthick sheet backed by aluminum the reflection coefficient is about −30 db at normal incidence and rises to −20 db at an incident angle of 60°. Beyond 60° the rubber is of little value in reducing the reflectivity. The results obtained are in good agreement with those expected from the theoretical treatment when modified for reflections from the back surface and the phase difficulties previously described by the author.