Q:  What is the NRC rating of a fiber glass batt?

A:  An NRC (Noise Reduction Coefficient) is a single number rating that is used to describe how well a material absorbs sound. A material with an NRC of 0.70 would absorb approximately 70% of the sound and reflect the remaining 30%. The NRC value is measured according to ASTM test method C 423 "Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method" by measuring the reduction in reverberation time with the use of the material. This test applies only to materials that are exposed to the sound source as installed. Because fiber glass batts are typically installed within a wall cavity, the NRC rating would not apply. Generally speaking, unfaced fiber glass batt thickness' greater than 2 inches would have an NRC of 1.0.