I have Googled and researched but not come up with a yes or no answer. The sites all say radiant barriers reflect heat/energy "like a mirror reflects light." It would seem common sense that mirrors would reflect heat/energy, too, but when the grandkids ask, I want the correct answer. I see this question coming up along with solar heating, swamp coolers, etc. Before I let them move a heavy spare mirror to the south side of the dog house to test it out, it would be nice to know whether it is worth it or not.