The “R” Value Fairy Tale

The R-Value is a modern fairy tale. It is a fairy tale that has been so touted to the American consumer that it now has a chiseled in-stone status. The saddest part of this fairy tale is that the R-Value by itself is almost a worthless number. The R-Value obviously favors fiberglass insulation.

As it is currently used, an R-Value is a number that is supposed to indicate a material’s ability to resist heat loss. It is derived by taking the K-Value of a product and dividing it into the number 1. The K-Value is the actual measurement of heat transferred through a specific material

Imagine the R-Value of an insulation after it has been submerged in water or at 20 miler per hour winds blowing through it. In these scenarios, the R-Value of fiberglass insulation goes to zero. Those same conditions barely affect solid insulation. R-Value numbers are misleading, meaningless numbers unless other characteristics are taken into consideration.

There are building codes in place mandating R-Values of 20s, 30s, even 40s. A fiberglass insulation of R25 in an improperly sealed house will allow wind to blow through it as if there were no insulation at all. Maybe the R-Value is accurate when the material is lab tested, but a lab environment may not even remotely duplicate conditions in the real world.

Consequently, we must start asking for some additional dimensions to our insulation. We need to know its resistance to air penetration, to free water, and to vapor drive. We must begin demanding the R-Value of an insulating material after it is subjected to real world conditions.

Experience has taught that R-Value tables can be used as indicators, but they need modifications to make them equal to real world conditions. Allowances must be made; they must show equivalents. These equivalents should indicate that one inch of spray-in-place urethane equals 4″ of fiberglass in normal installations. These tables should define degradation of insulations in real world conditions. Only then will the R-Value Fairy Tale become a real world success story.


A home insulated with fiberglass, on average, with all its doors and windows closed has a combination of air leaks equal to the size of an open door. Even if the home is perfectly insulated, fiberglass still does not stop air from moving vertically through the insulation itself, in ceilings or walls.

The best known insulation is solid insulation. Solid insulation performs far better than fiber insulators, especially when wind and moisture are involved. Spray-in-place Polyurethane Insulation is the only insulation used that absolutely protects itself from air infiltration. The bonding of the spray plus the expansion of the material creates a total seal.


We are told, with very good reason, that insulation should have a vapor barrier on the warm side. In theory, vapor barriers stop most of the moisture from passing, but not all. Small amounts of moisture move into fiber insulation and accumulates as temperatures fluctuate causing huge problems. Eventually, it could total buckets of water saturating the fiberglass.





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