Sealing Ceiling Boxes

Hello:
I have a 30 year old ranch house in New Jersey. I'm planning on continuing the previously started task of sealing all opensing from the living spaces into the attic for air infiltration.
I understand about caulking/sealing all wires, pipes and such. What I'm not clear on is how to seal the electrical boxes that my ceiling fans are mounted to?
I have a ceiling mounted fans or light fixtures in most of the rooms around the house, and there are gaps around the boxes. I know I can caulk/foam these gaps but what about all the individual holes in the boxes themselves? The boxes are a mix of metal and plastic boxes.
Can I lay some poly sheet over the box and lay the insulation over/around it? I hesitate to do this because at least 2 of the fixtures are mounted directly to the boxes (not ceiling fans or pendant lights) and there might be heat build up.
I see a lot of discussion on this subject for sidewall application, but very little for ceilings.
Any help would be appreciated.
Jim
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Anything used inside the electrical box should be fire rated. IMO
I would not use anything that is not fire resistant above a electrical box. I just insulated my attic with blown cellulose insulation. I just made sure that all the covers were on and I could still find the junction boxes. The light boxes got a new layer of insulation over them.
I doubt that all of your ceiling boxes leak that much air, compared with opening a door to enter or exit your home.
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Instead of plastic sheet, there are clear plastic vapor barrier 'boxes' that you can get to cover over these metal boxes. They re designed to keep the insulation from lying directly on the box yet will effectively seal the air infiltration. You may have to slice them open along one side to get them to wrap around the romex wires entering the box, you can then tape up the cuts you made with red "Tuck" tape and replace the insulation.
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Thanks for the replys. I'll check with my local Borg to see if they have those. Otherwise I'll have to check with my local electrician supply houses to see if they carry these.
Jim
Rudy wrote:

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