R-value (insulation) contain no trapped CFCs or HFCs (e.g., half-pound low density foams). On certain brands, twenty-year tests have shown no shrinkage or reduction in insulating value. This has led to controversy as how to rate the insulation of these products. Many manufacturers will rate the R-value at the time of manufacture; critics argue that a more fair assessment would be its settled value. The foam industry adopted the LTTR (Long-Term Thermal Resistance) method, which rates the R-value based on a 15-year weighted average. However, the LTTR effectively provides only an eight-year aged R-value, short in the scale of a building that
R-value (insulation) formula_1 divided by the R-value and then multiplied by the surface area of the object's side gives the "total rate of heat flow through the object" (as measured in Watts or in BTUs per hour). Moreover, as long as the materials involved are dense solids in direct mutual contact, R-values are additive; for example, the total R-value of an object composed of several layers of material is the sum of the R-values of the individual Note that the R-value is the building industry term for what is in other contexts called ″thermal resistance per unit It is sometimes denoted RSI-value