Thermal Resistance Value. R-Value is the imperial system unit of measurement (ft2·°F·h/BTU) of a material’s thermal resistance (i.e. how good it is at resisting heat flow by conduction). The higher the resistance value, the slower the rate of heat transfer through the material. Insulation materials are measured in R-Value. To convert an R-Value to an RSI Value (metric system), divide the R-Value by 5.678.
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