Critical Radiant Flux Product specifications for cellulose and mineral fiber loose fills as well as for mineral fiber blankets include a requirement called critical radiant flux. The term radiant flux means energy radiating from a hot surface. An example of this is heat energy radiating downward from hot roof sheathing onto attic floor insulation. The critical radiant flux of an insulation is the radiant energy level which enables a flame to spread across an insulation's surface. The test method used to determine critical radiant flux is ASTM E-970.
Higher numbers indicate better sound insulation performance.
STC tests are conducted in accordance with ASTM E90. A single number rating that indicates the sound absorbing characteristic of a material. The NRC rating is determined in accordance with ASTM C423. Greatest usage is with acoustical material such as acoustical ceiling tile. As with STC ratings, a higher number indicates better performance.