3M Peltor Optime 105 Cap-Mount Earmuffs feature double-shell technology to provide effective hearing protection. For noise levels up to 105 dBA, these cap attached with double-shell technology to provide effective hearing protectionNoise Reduction Rating (NRR)*: 27 dB. CSA Class AL*The NRR may overestimate the hearing protection provided during typical use. 3M recommends reducing the NRR according to the authority in your juristiction or reduce by 50-Percent for estimating the amount of noise reduction provided.3M is Leading the Advancement of Hearing Conservation.