ASTM C423 is the industry recognized test for evaluating the sound absorption of a building material. The test report lists the Noise Reduction Coefficient (NRC), which is typically between a range of “1” and “0”. If the material achieves a "1", it is said to have 100% absorption (like an open window). If the material receives a "0", it is said to be perfectly reflective. If a fabric has an NRC rating of .65, it means that 65% of the sound energy that contacts the fabric is absorbed, rather than reflected.