For loudest noise levels up to 101 dBA. Optime 101 earmuffs are designed for maximum attenuation in severe noise environments that have assessed levels of up to 101 dBA. Broad ear cushions provide excellent seal and low pressure for comfort. Cap mounted can be worn in three positions: in use, at rest (flipped up away from ears) and storage snapped against the top of hard hat. NRR 24dB. Tested to ANSI S3.19-1974 standard. Sold by the each.