Factors controlling the sound attenuation provided by earmuffs are analyzed and an upper limit is estimated of the attenuation that can be expected from simple earmuffs without sacrificing comfort. Further discussion concerns the best dimensions of the earmuff and what can be achieved by adding one or more Helmholtz resonators. The sound attenuation provided by two different earmuffs was determined on 8 subjects in 3 sessions with a Bekesy audiometer. The experimental procedure is described in detail and the results are analyzed statistically. Special attention was paid to the changes in the listener''s threshold of audibility with increasing experience.