What is the purpose of foil-faced insulation boards and where should they be used?

• A. They reflect radiant heat and provide the main insulation for exterior walls.
• B. They are the primary insulation for exterior walls.
• C. They are only used for decorative purposes.
• D. They absorb moisture to improve insulation.

Answer: (B)

Foil-faced insulation boards are designed to provide insulation while also acting as a radiant barrier. The foil facing reflects radiant heat, helping to reduce heat gain in the summer and heat loss in the winter, while the board itself supplies the main thermal resistance. When used on exterior walls, they create a continuous insulating layer on the outside of the structural frame, making them the primary insulation for that wall assembly in this context. They can also contribute to moisture control and act as a vapor barrier if installed with proper sealing around edges. They are not for decorative purposes, and they don’t function by absorbing moisture to improve insulation.