insulating them helps keep them from absorbing heat from the room.Why do you want to insulate? Are your res temps to high?
Foil facing out or in?
my buckets are all foil facing out, but my brain keeps telling me the foil should be holding the cool in by being up against the wall of the tank/bucket...
Foil backed 5mm foam, not just foil....
I've had DWC water temps below 70F in rooms that were +80F thanks to Reflectix/pipe insulation, a 4" duct fan blowing on the reservoir, (blowing air through a hole in the reservoir lid, with many small holes on the side walls for the air to exhaust out of the reservoir) and using waterfalls rather than airstones to generate dissolved oxygen.