These Peltor Optime 105 Series Earmuffs are perfect for extreme noise levels up to 105 dBA. Developed for the ultimate protection in the most demanding noise environments, the Optime 105 features added mass and volume, plus a unique "double shell" ear cup design (two cups connected via a foam inner layer to reduce structural resonances) to provide the maximum in noise reduction throughout the full range of low and high frequencies. Noise Reduction Rating (NRR)*: 27 dB. CSA Class AL . ANSI S3.19-1974/CSA Z94.2.