They have a through channel with a filter allowing  speech frequency sounds to be heard, but filter out the damaging middle-high frequencies.

Because of the through channel in the “ear plug” a person is not completely isolated from his/her surroundings and conversations and warning signals may be heard.

As custom-moulded earplugs are made from a soft silicone rubber, they are a suitable fit to each ear, thus alleviating any problems of poor fit or discomfort, giving laboratory attenuation in the ‘real world.’

Custom-made earplugs such as Noisebreakers can be comfortably worn under helmets or breathing apparatus. With a long life expectancy and no moving parts to wear out, such products are cost effective over time.