I'm going to insulate the 6" round metal heating ducts in my crawlspace, and I have pretty good access. It's the SF bay area, so it doesn't get very cold. Is there a reason to choose taped fiberglass bats vs fiberglass tubes when insulating heating ducts? Or is there a better choice?

It seems like it will be relatively easy to use the fiberglass tubes, but I'm looking for other people's experience doing this.

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    R-value would be the main consideration. Aside from that you need to look and how easy/difficult it is to install one versus the other. Last but not least, durability. Will a taped joint outlast a continuous tube?
    – MonkeyZeus
    Commented Aug 16, 2021 at 13:53

1 Answer 1


It turns out that the manufacturer of the fiberglass sleeves instructions say,

"For existing duct pipe up to 6 in. Dia - cut the jacket length wise (insulation is pre-cut) and wrap around the pipe."

They don't expect you to try and slip it over existing duct. Having installed this, I think it would be nearly impossible to slip this over the existing thin wrap of insulation, and the old insulation would not come off cleanly. I thought the fiberglass itself would be a tube, but it's just a long folded over bat inside a "metalized" tube. Pretty easy to slice open the tube and wrap the bat around the duct and then wrap the tube around the bat. Came out very nice!

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