[S-F]

If you have an IC AT can there is no reason not to literally cover it with foam. Completely. 100%. The drywall box is only for non IC rated cans. Making those boxes sucks. Just get new cans. If you wire them yourself it's less work than making those damn boxes and it works a LOT better. As to degrading spray foam: I only use two kinds of spray foam. One is for windows and doors, and I ONLY use it for windows and doors if I can help it. Sometimes the bean counters order cases of the stuff and that's all I have to use, and that sucks because it's lame stuff. The other is fire rated. It is code rated as a fire block between floors and the like but it's not ASTM E136 rated so you can't put it against a hot pipe or a chimney or something like that. If it gets too hot it will melt (seen it). There really is no reason to get any other kind of foam (Unless you are doing a window or door). I'm not sure about the consumer price but with a contractor account at Tiger Foam the price of fire rated and non fire rated foam is the same.
@ beatr911. Don't stop moisture movement. You want the house to be moisture permeable but air impermeable. The other day someone opened up my dishwasher. I have never used it to wash dishes but y son likes to "play" with it. It gets 1/2 filled with water and then after a couple weeks it gets plain rank. Like a sewer. Then I have to run it just to get the swamp out. The point is that we didn't know all of the fury of hell was festering in there. because it was vapor impermeable. Let it "breathe" moisture but not air. You don't want moisture condensing anywhere in your house except in you condensing dryer or boiler.