Foil faced insulation must have the foil side exposed to what condition to be effective?

• A. No air space
• B. An air space of 1 inch or more
• C. Direct contact with framing
• D. Direct contact with drywall

Answer: (B)

Foil-faced insulation works as a radiant barrier, and its effectiveness hinges on having an air space in front of the foil. The reflective surface bounces radiant heat back when heat moves across an air boundary, not when the foil is pressed against a solid surface. An air gap of about 1 inch or more minimizes heat transfer by radiation and helps prevent heat from traveling directly through conduction along the surface. If the foil is in direct contact with framing or drywall, that conduction path bypasses the reflective property, greatly reducing the barrier’s performance. So the foil side should face an air space of at least about 1 inch to work effectively.