I want to make recessed lights that are already installed in ceilings airtight. There is no access to the recessed space except through the opening into which the lights fit. Some lights are in exterior ceilings and I live in a moderate Pacific north-west climate so am concerned about creating a vapour barrier as well.

I was thinking of using a reflective wrap or the like that can be rolled up and stuffed through the hole and then affixed to the top and side of the joist cavity using staples and then sealed with spray foam.

Any thoughts?