Anechoic rooms are widely used in industrial testing and research on acoustic transducers and materials. The paper describes a chamber, designed and built at the University of Bradford for the dual purpose of research and teaching. The chamber designed was of necessity of small inside dimensions, and this fact dictated that the lining material had to be of high efficiency in order to leave the maximum usable internal volume. The acoustic properties of fibrous absorbers are discussed and a description of the methods used to classify fibrous material is given. The results of tests on several fibrous absorbers are presented, and the development of a highly efficient exponentially graded density configuration, using natural wool fibres or their equivalent, is described. The methods adopted in the Bradford University chamber to incorporate this favourable lining method are illustrated. The authors conclude by showing that the chamber, built as described, provides a highly satisfactory and economical solution to the problem.