Insulation is rated in terms of thermal
resistance, called R-value, which indicates the resistance to heat flow. The
higher the R-value, the greater the insulating effectiveness. The R-value
of thermal insulation depends on the type of material, its thickness, and
density. In calculating the R-value of a multi-layered installation, the
R-values of the individual layers are added. Installing more insulation in your
home increases R-value and the resistance to heat flow.
Common insulations and there R-Values
|
Insulation type |
R-value per inch of thickness |
|
Fiber glass blanket or batt |
2.9 to 3.8 (use 3.2) |
|
High performance fiber glass blanket
or batt |
3.7 to 4.3 (use 3.8) |
|
Loose-fill fiber glass |
2.3 to 2.7 (use 2.5) |
|
Loose-fill rock wool |
2.7 to 3.0 (use 2.8) |
|
Loose-fill cellulose |
3.4 to 3.7 (use 3.5) |
|
Perlite or vermiculite |
2.4 to 3.7 (use 2.7) |
|
Expanded polystyrene board |
3.6 to 4 (use 3.8) |
|
Extruded polystyrene board |
4.5 to 5 (use 4.8) |
|
Polyisocyanurate board, unfaced |
5.6 to 6.3 (use 5.8) |
|
Polyisocyanurate board, foil-faced |
7 |
|
Spray polyurethane foam |
5.6 to 6.3 (use 5.9) |
|