1/4" Acrylic dB Reduction:

SORBER NRC Ratings:

The Noise Reduction Coeffecient (NRC) is a single-number index determined in a lab test and used for rating how absorptive a particular material is. This industry standard ranges from zero (perfectly reflective)
to 1 (perfectly absorptive). It is simply the average of the mid-frequency sound absorption coefficients
(250, 500, 1000 and 2000 Hertz) rounded to the nearest 5%.

Based on the testing methodology, and depending upon the material's shape or surface area, some products can test at an NRC above 1.