3M Peltor Optime 101 Cap-Mount Earmuffs, Hearing Conservation H7P3E-01 For noise levels up to 101 dBA, these cap-mount earmuffs provide effective hearing protection Dielectric Cap-mounted design allows for easy use with most hard hats. Liquid/foam filled ear cushions. Noise Reduction Rating (NRR)*: 24 dB. Class A *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. 3M is Leading the Advancement of Hearing Conservation.