NRC Data Table:

You can judge a foam’s absorptive effectiveness by studying its NRC (Noise Reduction Coefficient), a single number average of a foam’s absorption in what was determined long ago to be the most important range. The federally mandated test (ASTM C423) is standardized to cover frequencies between 125Hz and 4000Hz, but when calculating an NRC, only the coefficients from 250Hz to 2000Hz are used to help alleviate the possibility of testing errors.
All of our foam products are tested at an independent, unbiased acoustical laboratory – the oldest, most reliable lab in the country. We insist on using only the very best testing facility because we believe our customers deserve the most accurate absorption coefficient information possible.

NRC Of Flat: