In the construction industry, the term R-value refers to a material's thermal resistance. Basically, if a substance can hold very different heats on either side of it, it has a high R-value. The quantity is measured by the inch -- the more insulation you stack, the greater its combined R-value. It would take quite a stack of traditional concrete to equal an inch of Air Krete.
For Air Krete, the R-value is 3.9 per inch. Compare this to R-values of 0.8 for concrete without the trapped air, 1.45 for straw bales and around 3.1 for most types of high-density fiberglass batts, and Air Krete comes out on top [source: Johns Manville Insulation].