In the construction of ear plugs the chief problem is to combine the necessary sound insulation with comfort and sufficient speech intelligibility. Ear plugs are described which fulfill these requirements to a reasonable degree. They can be used for the attenuation of all audible frequencies or, with minor adaptation, as low‐pass filters attenuating the more dangerous high frequencies only. For maximum speech intelligibility, both kinds of sound insulation are adequate for steady noises, whereas the low‐pass filter is better for intermittent noises, detonations, and noise that can be interrupted to permit communication. Extensive experiments in industry and the armed forces have shown that low‐pass filters with a cut‐off frequency of 1000 cps provide sufficient hearing protection in most situations.