Polyurethane is a highly efficient insulator. For every two
inches of polyurethane foam, this much of another insulating material
would be needed for equivalent insulatin performance: "U-value" (or U-factor) measures heat transfer
through insulation or a building component over time, under standardized
conditions. Since it's an inverse measurement to R-value (R = 1/U),
a low U-value number indicates a superior insulator.
| Insulation Material | R-value Range | Thickness to match 2" |
| Polyurethane Foam | R 5.6 - 8.0 /inch | 2 inches |
| Polystyrene | R 3.8 - 5.0 / inch | 3.1 inches |
| Cellulose | R 3.6 - 3.8 / inch | 3.7 inches |
| Rock & Glass wool | R 2.9 - 3.8 / inch | 4.0 inches |
| OSB Sheathing | R 1.25 / inch | 10.9 inches |
| Plywood | R 1.25 / inch | 10.9 inches |
| Concrete Block | R 0.25 / inch | 54 inches |
| Brick | R 0.2 / inch | 68 inches |
Sprayed Polyurethane Foam (SPF) will have
an R-Value of 7.14 when it is newly installed. After it ages a few
months, the R-Value will reduce to somewhere around 6.88. The C-value
(C) is a measure of the Thermal Conductance of the material and is the reciprocal of R, or
C is determined only when the Thermal Conductivity (k) of a
material is known.
