R-value(redirected from R value)
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A measure of the capacity of a material, such as insulation, to impede heat flow, with increasing values indicating a greater capacity. Also called R-factor.
a measure of the resistance of an insulating or building material to heat flow, expressed as R-11, R-20, and so on; the higher the number, the greater the resistance to heat flow. Compare U-value.
[1945–50; R, symbol for resistance]