Sound reduction membranes as part of a floor/ceiling system are rated in various classifications. The most accurate are based on ASTM tests that measure how sound transmission is affected by underlayment materials over a variety of substrates. Perhaps the most useful measure of comparison is the Delta Impact Insulation Class (Delta IIC or ∆db, a laboratory value for the amount of sound reduction directly contributed by the membrane itself. The ∆db can be used to compare the sound reduction properties of underlayment mebranes made of different materials and thicknesses. PROFLEX TM products are tested under the independent National Voluntary Laboratory Accreditation Program (NVLAP).