Why use foil-faced insulation?
Ways of Heat TransferIn order to explain why use foil insulation, firstly we need to look at how heat is transferred. There are three main methods:
Heat loss from convection occurs through the movement of air while it’s suitable design and effective workmanship. Insulation works to prevent heat loss through conduction and materials chosen to make insulation have a low λ value or thermal conductivity. This means that they are good at preventing heat loss from conduction.It is the last method of heat transfer – radiation -- that is addressed by adding foil facings to the insulation.RadiationRadiation is the process by which heat is emitted from a body and transmitted across space as energy. Radiation does not require any intermediate medium such as air for its transfer; it can readily take place across a vacuum.
For a clear unventilated cavity, adding a low emissivity foil facing to at least one side of the cavity will improve, maybe even triple the thermal resistance. This means that adding a foil facing to insulation can significantly improve the U-value of the construction. This enables a thinner insulation to be used to achieve the same U-value.