Noun
English Wikipedia has an article on:r-valueWikipedia
r-value (plural r-values)
A measure of thermal resistance used in domestic insulation.
Insulation and weatherstrips But there are very few door models with an R-value close to 10 (which is far less than the R-40 walls or the R-50 ceilings of super-insulated buildings – Passive Solar and Zero Energy Buildings ). Source: Internet
The construction industry makes use of units such as the R-value (resistance) and the U-value (conductivity). Source: Internet