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Is Bubble Wrap Duct Insulation a Good Idea?

Although reflective layers can be effective when installed correctly, they aren't the best way to insulate ducts

Is bubble wrap a good insulation material?

Lora’s question seemed innocent enough, but it was enough to touch off a war of words and prove that building science isn’t always as dryly academic as you might guess. It can, in fact, get downright cantankerous.

Lora’s HVAC installer wanted to insulate the ducts in her house with double-wrapped bubble wrap “as a cheaper way to achieve R-6.” Fine, she thought, but does the stuff really work?

It “sort of works,” said Green Building Advisor Michael Chandler, but a better option is installing foil-faced duct insulation (not foil-faced bubble wrap) after ducts have been sealed with mastic and checked for air-tightness, preferably by an independent tester. Foil-faced bubble wrap “is not Energy Star or Manual D approved,” he wrote, “and is generally viewed as snake oil by reputable builders.”

Senior editor Martin Holladay was next, picking up the “snake oil” theme and going on to say any claim that bubble wrap is the equivalent of R-6 duct insulation is a “scam and a fraud.” He specifically cited a company called Reflectix, which makes a 5/16-inch thick material consisting of bubble-wrap plastic between layers of reflective material. “According to ASTM C518 tests commissioned by Reflectix, the product has an R-value of 1.04,” Holladay wrote. “(Reflectix does not mention this R-value of 1.04 on its Web site; however, it can be found in a laboratory report available from the company on request.)”

Installation is the key to performance

As Holladay points out, the R-6 insulating value is based on the complete assembly, not the material alone. In tests conducted by the ICC Evaluation Service, the bubble wrap was installed over a continuous 3/4-inch air space around the duct. “In fact,” he added, “the reported R-6 derives to a large extent from the air space, not the Reflectix.”

An installer would have to apply 3/4-inch spacers every two feet along the ducts to get the intended performance. “Most HVAC contractors are likely to consider the construction of a three-dimensional site-built air space around installed ductwork to be labor-intensive and awkward, especially considering the difficulties of working around hanger straps,” Holladay wrote. “Moreover, the R-value of the assembly depends on the long-term maintenance of the 3/4-inch air space; if the Reflectix ever sags, the R-value of the assembly will drop.”

Maintaining an air space on one side of a reflective barrier is essential to performance, Robert Riversong added. “Reflective ‘insulations’ work best with downward-flowing heat, such as from roofs to attics or from floor to cellar,” he said. “It’s possible to get as much as R-8 or R-9 in a floor with one foil surface enclosing a 4″ air space. As soon as you tilt the air space above 45° toward vertical, internal convection undermines the radiant benefit.”

Although the physics of radiant barriers is relatively simple, he added, “much of the manufacturer promotion is hype.”

If it’s good enough for space suits, why not ducts?

The “hype” and “snake oil” insinuations were too much for Kelly Myers of RFoil Insulation Products. “Contrary to the above comments, a foil-faced bubble insulation is a very good way to insulate ductwork, especially in hot climates,” Myers said. “Most people don’t understand how an reflective-faced material can insulate…”

Myers said his industry has been guilty of making “false or exaggerated performance claims” or recommending it for inappropriate situations.

“I’ve seen foil insulation marketed for applications where I know the product will not perform, such as where no airspace exists. These are times when foil manufacturers have to accept that traditional insulation is the better choice. Our industry hasn’t done that very well,” Myers said.

Even so, bubble wrap duct insulation is an effective insulator, he said, and not susceptible to the same condensation and mold problems as fiber-based duct insulation.

Then there’s the endorsement from outer space. Myers pointed out that foil is used in space suits because it reflects the intense radiant energy of space more effectively than a fiber insulation. That alone should be some indication the product works, Myers argued, and besides, conventional tests that measure R-values are misleading because they don’t take the transfer of radiant energy into account.

Some users of bubble wrap liked the results

The reference to the benefits of foil in space touched off an exchange of verbal broadsides (including claims that one thread contributor “had left a good part of [his] gray matter in outer space”) and a detailed debate over the nuances of R-value testing and physics.

There were, however, several first-person reports of bubble wrap being used successfully on ducts, the point of Lora’s original question.

Gary, for example, said what was apparently bubble wrap was installed around ducts that ran over a computer room where air conditioning equipment ran around the clock. Before the installation, condensation on cold ducts was a serious problem. Afterward, no condensation. “I can’t speak to R value or anything other than it provided what was necessary for the application we needed it for,” he said.

Likewise, Michael T. Lauer reported significant energy savings after wrapping existing R-6 duct insulation with a layer of bubble wrap radiant barrier in an attic.

In the end, Riversong may have summed up the efficiency of bubble wrap radiant barriers most succinctly: “It’s not a scam,” he wrote, “but it has limited value and only when used in the appropriate applications.”

11 Comments

  1. Armando Cobo | | #1

    How ironic...
    How ironic that as read this great article by Scott, on the same webpage there is an ad by Lo/Mit Spray-on Barrier. Maybe we should jump from the frying pan to the fire!!! It all “boils” down to $$$$….

  2. User avater
    Daniel Morrison | | #2

    It boils down to keywords, Armondo
    Google serves the ads based on what the article is about. This may not be the best value for the people buying the ads though, huh?

  3. Harry Corey | | #3

    reflectix
    I read and understand that using bubble wrap as duct insulation without an air gap doesn't work. What if it is installed on the bottom of the floor joist with a 4" space between it and the fiberglass insulation. Is that still a waste of time. Unfortunately I have already purchased the bubble wrap and would like to be sure it is an ineffective product before returning it. To bad I found out about this site at the wrong time.

  4. User avater GBA Editor
    Martin Holladay | | #4

    Response to Harry Corey
    Harry Corey,
    Reflectix has an R-value of about R-1. If it is installed adjacent to an air space, it can raise the R-value of the air space up to about R-3. That's not much.

    You can get much more insulating value per dollar by buying real insulation. For example, $100 of XPS or EPS foam will do a much better job of insulating than $100 of Reflectix.

    So if the retailer who sold you the Reflectix will take it back and give you a refund, by all means return it.

  5. PoodleHead Mikey | | #5

    The duct feels cooler with bubble wrap - why is that?
    My heating ducts were warm to the touch.

    I installed some bubble-type duct insulation because I think fiberglass is the asbestos of the future.

    Now when I touch the outside of the insulated duct it is cool to the touch.

    I realize that this is not exactly lab-tested proof - but what other explanation is there except that the bubble wrap in insulating the air duct?

    PHM
    --------

  6. User avater GBA Editor
    Martin Holladay | | #6

    Response to PoodleHead Mikey
    PoodleHead,
    You're right -- the bubble wrap is insulating the duct. It probably has an R-value of R-1.

    It just isn't insulating very well. In most areas of the country, R-6 or R-8 duct insulation is standard (and often required by code).

  7. Kohta Ueno | | #7

    Infrared Images of Bubble-Foil Wrap Duct Insulation
    I was recently in an attic of a recent-construction multifamily building; I noticed that they had used two layers of bubble-foil wrap duct insulation on the duct trunks, and a fiberglass wrap on the runouts. Both of these ducts were sheet metal, but with some insulated flex at runouts. The bubble wrap was installed with no air gap between the bubble wrap and the sheet metal duct.

    I happened to have my infrared camera with me in the attic. Of course, foil surfaces throw off temperature measurements by infrared, due to emissivity effects (that's why you can set the emissivity value on IR cameras). However, the ducts were both covered with a layer of cellulose insulation, which essentially negates the effect of low E coatings.

    You can see the difference in surface temperatures--the bubble wrap foil duct has a much warmer surface temperature than the fiberglass wrapped ducts. So it looks to me like two layers of bubble foil wrap is performing worse than an R-6 fiberglass duct wrap.

    Yes, I know, the ideal experiment would have been to clean off the ducts and run a strip of masking tape down the foil jackets of both to get a same-emissivity surface temperature test. However, I was trying to get an investigation done, not get duct surface temperatures.

    Also, as a side note--if the low-E foil coating had a significant effect on my surface temperatures, it should make surfaces "look" colder, not warmer, to an infrared camera.

  8. User avater GBA Editor
    Martin Holladay | | #8

    Response to Kohta Ueno
    Kohta,
    Thanks for sharing your revealing photos. Your conclusion -- "the bubble-wrap foil duct has a much warmer surface temperature than the fiberglass-wrapped ducts" -- is consistent with what one might expect from the dismally low R-value of bubble wrap.

    You didn't mention whether the photos were taken during heating season or cooling season -- but I assume that these ducts were delivering heated air from a furnace or heat pump, not cool air from an air conditioner.

  9. Kohta Ueno | | #9

    Duct Air Temperature

    You didn't mention whether the photos were taken during heating season or cooling season -- but I assume that these ducts were delivering heated air from a furnace or heat pump, not cool air from an air conditioner.

    Sorry I didn't make that explicit--this photo was taken on a 30-40 F outdoor temperature day in New England; all HVAC equipment was running in heating mode. Heating was provided by 90%+ sealed-combustion gas furnaces.

  10. HD3500 | | #10

    Last year we finished off an attic room over our garage and had duct work added from our existing HVAC system to the new space. The contractor looked at the size of the unit and said it should handle the additional approx 230 sq ft of space. The system works somewhat... but it's definitely warmer in that room during the summer than the rest of the upstairs. My question from the start was with the type of insulation they used for the duct work, which was the thin bubble wrap type around the main trunk line. The main house has fiberglass insulation around the main trunk line. Both spaces, new and old, used fiberglass flex lines. My question is: Can I add fiberglass insulation over the existing foil bubble wrap to up the r-value and help the system handle the additional space footage? I'm concerned about the cool air being lost to the extreme temperatures in the attic. Or would that be a waste of money. Our house is in the southern Maryland region.
    Thanks for any insight,
    HD

  11. User avater GBA Editor
    Martin Holladay | | #11

    HD,
    Q. "Can I add fiberglass insulation over the existing foil bubble wrap to up the r-value and help the system handle the additional space footage?"

    A. Yes. The existing bubble wrap has such a low R-value that it's basically worthless as insulation.

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