When worn correctly, foam HPDs attenuate (reduce) sound levels reaching the ear. Noise reduction ratings (NRRs) for foam HPDs range from 20 to 35 dB and provide greater attenuation at high frequencies than at low frequencies. Most foam HPDs are designed for one-time use.

Custom-molded HPDs provide equal ("flat") sound attenuation for high and low frequencies and are
re-usable. They have NRRs of 15 to 25 dB and are designed for people who rely on their ability to hear high and low frequencies without distortion. These HPDs are custom-made by licensed hearing healthcare providers and offer a comfortable form fit and long-term wear.

Ear muff HPDs are easy to take on and off but require a solid shell and acoustic seal around the ear to effectively attenuate noise.