It gets a little tricky, but we will attempt to explain it in simple terms.

Radiant heat by definition is heat transfer from one object (the hot object) to another object (the cooler object) by NON-CONTACT.

We really wish you could put foil between shingles and roofing felt or roof deck because we would sell a ton more foil. However, physics is physics – and it just won’t work.

If you take radiant barrier foil and sandwich it between the shingles and roof felt, you have now created one solid assembly. Aluminum is a unique element, it is both reflective and very conductive. This is one example why we cook with aluminum cookware; it conducts heat very well, which is good for cooking, but not so good for living spaces.

Here is an illustration most people can relate to: Have you ever picked up a hot potato that was wrapped with foil? It feels super hot, right? Why is that? Well, when your skin touches the foil it creates direct path (there is no longer an air gap, just the foil touching your skin) so the heat flows directly into your hand, making your hand very hot. The idea is that heat doesn’t care what objects it’s traveling through to carry heat flow, as long as objects are touching and there is no air space, the heat might as well be traveling through one, large object.

When an air gap is present, the heat is then forced to convert to its radiant form so it can jump the gap and continue traveling via conduction.