THERE ARE MAINLY TWO DIFFERENT METHODS OF MEASURING AND CALCULATING THE LEVEL OF PROTECTION:NRR – Noise Reduction Rating –  as per the US standard.SNR – Single Number Rating –  as per the EU standard.The difference between the SNR and NRR is because of two different calculations of the variations in a broad population. Meaning, since people have differently shaped ear-canals, or they insert and use the earplugs differently – the protection can be higher or lower. The NRR includes a larger variance factor and is always lower than both the SNR and the averaged values.