3M™ Peltor™ Optime™ 105 behind-the-head earmuffs features low-profile earcups that fit well with most helmets, Feature double-shell technology for effective hearing protection. Patented Twin-Cup™ design has soft, foam-filled earmuff cushions. Behind the head design allows for easy use with hard hats. Liquid/foam filled earmuff cushions. Noise Reduction Rating (NRR)*: 29 dB. CSA Class AL.*The NRR may overestimate the hearing protection provided during typical use. 3M recommends reducing the NRR by 50% for estimating the amount of noise reduction provided.