In order to be effective, foil faced insulation must have the foil side ____________.

• A. exposed to a 1 inch or more air space
• B. facing the interior
• C. against the wall
• D. touching another layer

Answer: (A)

Foil-faced insulation acts as a radiant barrier, so the shiny foil must have space around it to work. The reflective surface shoves heat away by radiation, but that only happens effectively if there’s an air gap next to the foil. An air space of about an inch or more prevents heat from transferring directly through contact and conduction into adjacent materials, allowing the foil to bounce heat back rather than soak it in. When the foil is pressed against a wall, against another layer, or sealed with no air gap, the heat largely moves by conduction through the touching surfaces and the reflective benefit is greatly reduced. That’s why the foil side needs to be exposed to a 1 inch or larger air space.