Foil Bubble Wrap For Insulating Exterior Walls?

Q: What's your opinion on foil bubble wrap for insulating exterior walls? I installed some on the inside surfaces of the outside walls on my 50-year-old house. Even though this product carries no R-value rating, it's making the walls obviously warmer to the touch. Should I use it again?

A: I'm familiar with reflective foil barriers and I've used them before. They're an energy conservation product that works by 'shining' back the transfer of radiant energy as opposed to blocking the conductive transfer of heat, as happens with conventional foam and fiber insulation products. The reason reflective foil barriers don't typically carry R-values is because their numbers are so low -- usually less than R-1. And while this sounds laughably low, it doesn't mean that reflective foil barriers have nothing to offer. In fact, they do, though I'm convinced they work best in conjunction with more typical insulation materials.

Think of reflective foil insulation like a parasol at the beach on a sunny day. The R-value of the fabric itself is almost negligible, yet you remain obviously cooler in its shade. This is the benefit of radiant reflection. In retrofit applications such as yours, you'll get best results if you apply a one- or two-inch thick layer of rigid foam to the inside surfaces of exterior walls. Cover this with a layer of reflective foil barrier, then apply a fresh layer of drywall on top of everything. Anchor this drywall with screws that extend into the wall frame of the house, then finish the joints and screw heads with compound as usual. Since reflective foil barriers have only a small R-value on their own, they won't satisfy building code requirements for insulation. That said, they’re especially useful in reducing summer time room temperatures by reflecting heat from hot attic spaces. Simply lay the foil over top of existing insulation as it sits on the attic floor.

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