This is just a cutaway of a typical can installation. In an earlier tip we discussed sealing the can to the drywall from underneath. While that helps infiltration around the can it doesnt address through the can or the poor insulating value of the can. The picture above is typical of most can light installs. It is easy to see how much heat could leave through this setup. One builder I know threw buckets over the cans before the insulators came through. I've never fely like I had a great solution until recently. I was talking to a friend whos been in the trades for years, and his fix was to install a 12"x12"x12" duct board box over the light and caulked to the drywall. This is a simple fix. Duct board boxes can be made up by your local hvac contractor for around $20. The walls of the box are an inch thick so there is plenty of surface to caulk to the drywall. If your light is next to a cieling joist the duct board is easy to notch with a utility knife, just make sure you caulk between the notch and the joist. For less than $25 each light you have stopped the air leakage and significantly improved the r-value. Thanks Dave for a great idea.