R-value

[ ahr-val-yoo ]
/ ˈɑrˌvæl yu /

noun

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.

Origin of R-value

1945–50; R, symbol for resistance
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019