What Is R-Value?

r-value Insulation is needed for a structure to maintain an ideal interior temperature. Properly insulating your home makes its interior a pleasant environment to live or work in; significantly reduces your heating and cooling bill and makes your home ecologically friendly because you help conserve environmental resources.

In a nutshell, insulation is any type of material or substance that resists the transfer of energy (heat and cold). There are different types of insulation available in the market today but not all have the same level of effectiveness. Insulation materials are rated in terms of their thermal resistance called R-value. The R-value indicates the insulation material’s resistance to heat flow.  The R-value of any thermal insulation depends on the type of material, its density and its thickness.

The R-value is measured per square meter the amount of temperature difference in Kelvin degrees needed to transfer a watt of energy.  To simplify, an R-value of 1 will transfer one watt of energy per square meter and an R-value of 2 will transfer ½ watt of energy for one degree of difference. The higher the R-value, the greater its insulating capacity. When using multiple layers on insulation, the R-value of each layer is added for the total R-value.

The R-value is not the only factor to consider in insulation. The efficiency of an insulated floor, wall or ceiling also depends on where the installation is set up. Note that when insulation is compressed, it will not have its full R-value. For example, if you stuff a wall cavity with too much insulation, it will lose its effectiveness.

Here is a short list of known R-value of common insulating materials in a 6” wall.

  • Cellulose R-21
  • Fiberglass R-21
  • Urethane spray foam R-21
  • Poly-urethane spray foam R-42