Get airtight lights for those lights that will be in the framing that makes up your house's environmental envelope.
Example...in a cathedral ceiling (where, in my world, no penetrations are allowed), or in your top floor ceiling/attic floor platform.
Regardless, all cans should be IC-rated.
Air-tight usually means it's IC-rated, but IC-rated does not always mean that the can is air-tight.
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