The absorption of normal incident sound by a curtain hung flat before a wall depends on the flow resistivity and the weight of the material and the distance to the wall, as has been found experimentally and could be deduced theoretically. The same theory allows one to calculate the absorption for oblique incident and, also therefore, for statistical omnidirectional incident sound. The sound absorption thus calculated for many curtains with different flow resistivity, weight, and distance to the wall has been compared with the sound absorption as measured for these curtains hung flat at the mentioned distances to the wall in a reverberation chamber. An excellent agreement has been obtained. If the curtain is draped, the absorption also depends on the draping. If the “draping degree” is defined as the ratio of the apparent surface to the total undraped surface, it has been found experimentally that the amount of acoustical absorption introduced by the curtain into a reverberation chamber is for the midfrequencies inverse proportional to the fourth root of this “draping degree.”