Definitions for r-valueˈɑrˌvæl yu
Random House Webster's College Dictionary
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.
Category: Building Trades
Ref: Compare U-value.
Origin of R-value:
1945–50; R, symbol for resistance
Resistance-value - A measure of thermal resistance used in domestic insulation.