Recently I attended a seminar sponsored by a manufacturer of a foiled face insulation product. The presenter at the seminar claimed their insulation had an R value of R 14 for an 8mm thick foil faced material. It may be that the foil face provides the high R value that they claim but I’m suspicious. Do you have any thoughts on these insulation products?

You are wise to be suspicious of the R value claims of some foil-faced insulation products. For years there has been a commonly held opinion that these products are miracle insulators. Upon close scrutiny, most of these R value claims are often just hearsay and urban legends. The hard science often does not support the tradeshow sales pitches.

The reason for these discrepancies in R value estimates often comes from the methods used to determine R value when testing a product. In other words, one manufacturer will use vastly different benchmark criteria from another manufacturer, and then compare their product results to competitor’s products.  To be fair, all products should be compared to the same benchmarks for consumers to get a true and accurate R value comparison. Unfortunately, this is often not the case with these insulation products.

Here are some recent test results for one brand of foil–faced insulation. The long term thermal resistance of one inch (30mm) of this insulation ranges from R 3.75 to R 4.0. The foil facing does increase the radiant heat barrier performance of the insulation, but this foil face has little effect on the conductive heat loss of the insulation. For instance, an empty wall stud cavity with a 3/8 inch (8 mm) layer of one foil-faced product tested under ASTM procedures had a total thermal resistance of only R 5.2. So, you are wise to be wary of R value claims for some of these products. The R values are sometimes wildly exaggerated. If in doubt, research the testing procedures used to establish their R value claim. In my opinion, look for research that comes from an established independent testing agency like ASTM or WH for the most reliable and accurate test information.