The Noise Reduction Coefficient (NRC) represents the amount of sound energy absorbed by a surface where a value of zero (0) indicates perfect reflection and a value of one (1) indicates perfect absorption. Keep in mind that absorption does not imply eliminating sound. A product's NRC rating specifies the amount of sound that is not reflected. The methodology to measure NRC is specified by ASTM C423.
NRC is the arithmetic average of sound absorption at the frequencies listed in the table below. Values greater than one (1) may me attributed to the shape, thickness, and edge effects of the product tested.