The SNR value (Single Number Rating) is a European standard that allows you to compare the noise reduction levels of different hearing protectors. Independent laboratories test earplugs and earmuffs to determine the SNR value of an earplug.
In the United States, an NRR (Noise Reduction Rating) is used instead of an SNR. This standard is slightly stricter than the European standard. The higher these ratings, the more the hearing protection reduces noise. Both NRR and SNR ratings are often listed on Alpine product packaging.