Do you have damaged foil-backed foam board insulation in your house? If so, why did you leave it uncovered instead of finishing your construction? Never mind; no one wants to hear your excuses.

If you do have exposed foil-backed foam board insulation with damage, here is an interesting trick to help address the issue. The result is not perfect, but it restores some of the insulation properties and improves the appearance.

1. Cut a piece of aluminum foil slightly larger than the area to repair. It should be roughly an inch wider on each edge. The aluminum foil should be used dull side out.

2. Spray foam into the damaged area. The foam should be roughly equal in volume with the hole in the foam board. The foam will continue to expand a little over time, so do not overfill.

3. Put the foil on a flat stiff surface with the shiny side up, so the dull side will be out.

4. Gently angle the board up to be flat against the wall with the foil covering the damaged area. Press gently to shape the foam to the hole.

5. If the damage is spread across two panels that are not even, you can tape along the panel seam to pull the panels closer together and press the to halves separately.

6. Use clear packing tape to secure the patch in place. Work carefully to keep the foil unwrinkled. If needed, wipe excess foam from floor in front of patch. To keep the patch flat, check patch periodically over the next 30-60 minutes to press the board against it. The foam may continue to expand for at least a few hours after spraying.

It is not perfect by any means, but it was surprisingly effective for something we made up on the spur of the moment. Be aware that larger holes are harder to fill properly and tend to have a more lumpy appearance. The foam will continue to expand a small amount for more than the initial 30 to 60 minutes. Especially for larger holes, it can be useful to keep something flat against the wall with a heavy weight against it to force the expansion inwards instead of outwards.