R-Value, in essence, was derived for fiberglass insulation.  In the late 50's, when insulation became code to be installed in our homes, fiberglass insulation was the only insulation available.  In return, R-Value was established for fiberglass.

In order to better explain why R-Value was established for fiberglass, we need to look at the definition of R-Value and the three heat transfers that happen on any building or structure.

R-Value measures a material's resistance to heat flow.

Three Heat Transfers:

•   Conductive-transfer of heat flow through any given material.

•   Convection-air movement (EPA states 40% of monthly utility bills are contributed to air movement).

•   Radiation - rays from the sun.

Looking at the definition for R-Value and the three heat transfers that happen to any building, you see that fiberglass only reduces one of the three heat transfers that happens on a building which is conduction.  It does not stop convection or radiation.

Spray foam insulation stops or controls all three of the heat transfers that occur on any building or structure.  This is what makes spray foam insulation so effective by saving up to 50% on monthly utility bills, better indoor air quality and making the structure quieter.

A good example to compare R-Value and spray foam is:  When you go to McDonalds and get a 130 degree cup of hot coffee, what do they serve the coffee in?  Yes, a foam cup.  What do you think the R-Value of the foam cup is?  Maybe a .1.  Why doesn't the 130 degree hot coffee burn us with such a low R-Value?  It is because the foam cup stops all three of the heat transfers and not just one.