Noise Reduction Rating: NRR 21. Great for swimming. Seals out water. Reduces noise. Noise Reduction Rating. 21 decibels (when used as directed). The range of noise reduction ratings for existing hearing protectors is approximately 0 to 30 (higher numbers denote greater effectiveness). Federal law prohibits removal of this label prior to purchase. Label required by US EPA regulation 40 CFR part 211 subpart B. Sound Attenuation Data (ANSI Standard S3.19-1974) NRR 21. Test Frequencies (Hz) 125, 250, 500, 1000, 2000, 3150, 4000, 6300, 8000. Mean Attenuation (db) 25.1, 24.0, 22.3, 26.5, 36.0, 41.0, 40.8, 40.3, 40.3. Standard Deviation (db) 3.8, 3.5, 3.0, 3.1, 3.5, 3.8, 3.8, 3.3, 3.0. The attenuation values were obtained under laboratory conditions and are for comparison purposes only. The amount of protection afforded may differ depending on how the protectors are fitted and worn. The attenuation values in actual use may be lower.