Are Insulation R-Values a Good Measure of Insulation Performance?

Yes. The answer is simple, so this could be the shortest blog ever. However, given the misinformation that is out there it is worth explaining why R-value is in fact a good measure of thermal performance and dispelling some common misconceptions about it.

What R-value considers and what it doesn’t

We know that R-value measures resistance to heat flow, and there are three kinds of heat transfer to consider: conduction, convection and radiation. The FTC Rule on “Labeling and Advertising of Home Insulation” requires the R-values of typical insulation materials be based on measurements taken using one of four approved ASTM test standards[1].  These ASTM standards measure heat flux - which includes all three modes of heat transfer:  conduction, convection and radiation.   Despite this, there are claims in the market that R-value only considers one type of heat flow, namely conduction. Martin Holladay, writing for Green Building Advisor back in 2009, recognized and sought to dispel this misinformation in a very thoughtful article on this subject. Fast forward to today, May of 2016, and this same misinformation is being propagated, this time in Spray Foam Magazine’s May-June edition, which contains an article again claiming R-value only considers conduction and not convection or radiation. Same claim, still false.

Click here to read more about the relaibility of R-values to gauge thermal performance.