Does Reflectix “Big Bubble” insulation really achieve R-6?
I have seen several discussions here about bubble wrap insulation for ducts (some links below). However, they are all a couple years old, and they don’t seem to directly address one of Reflectix’s products. The older and smaller products were generally met with great skepticism because they claimed high R values without clarifying that the installation required an air gap between the duct and the bubble wrap.
I recently had new ducts installed with a new HVAC system, and my installer used Reflectix “Big Bubble” insulation directly around rigid metal trunks (and flex line for the runouts). From what I understand, this product differs from other bubble wraps in that it is thicker (~1 inch thick) and contains two layers of bubbles. This product specifically states on it in big red letters “R-8 WITH AIRSPACE” and “R-6.0 WITHOUT AIRSPACE.” The company’s website says “The product provides an R-8.0 when installed with a 0.75” air gap between the duct and the insulation, and R-6.0 when installed direct to the duct without a spacer.”
Since so many people seemed not to trust the claimed R values of other bubble wrap products, I’m wondering if anyone has any concerns with the claims about the “Big Bubble” product?
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Huhnra, dead air is about R-5.6/in, so if the air inside the bubbles remains perfectly still it indeed should perform at somewhere around R-5.6/in, which of course marketing people will round up to R-6.0. With the air films on all faces of the foil and the duct itself, plus the benefit of a 3/4" gap adjacent to a reflective surface, which may add about R-1 to the assembly, it might start to get close to R-8 in total. But there are a lot of fine points, and with Reflectix' history of obfuscation and outright lying, I think it's safe to assume the actual insulating value may be less than stated. It's curious that nowhere in their literature can I find what third party lab did their R-value testing; they list the proper ASTM test for the product and the testing agencies for other tests, but not for R-value.
I just sent an email to Reflectix, asking for a copy of the test report from the third-party lab (assuming that such a report exists) that shows the R-6 value of Big Bubble. If I get an answer, I'll report back.
Don't let your dinner get cold waiting for a response.
ASHRAE fundamentals has a plot of center-of-glass U-factor for triple-pane windows. For air-filled, 0.5" spacing, it's 0.17, which translates to 5.9 R-value. That includes about R-0.96 for the interior and exterior surface effects, so the R-value for the two air gaps with low-e is is about R-5. That's a reasonable estimate for what this product might do.
The R-5.6 Michael notes for dead air would be an upper limit for what might be possible if the bubble walls impede air circulation better than in a 0.5" air gap window, and the aluminized reflective layer completely stops radiation heat transfer. In the absence of a 3rd-party measurement, I would assume no more than R-5; even that might be a little optimistic, but it is a lot more plausible than some claims for thinner similar products.
There would be nothing wrong with it if it were cheap enough. I see it selling for $286 for a 4'x75' roll. R6 fiberglass duct insulation in the same size roll is $136 to $176. Perhaps the price premium can be justified if it's nicer to work with, but R-5 isn't much--it would be better to have two layers, and at that point the labor cost and the materials cost both go up.
I think we can safely conclude that Martin's dinner is unlikely to stay warm, even wrapped with Big Bubble.
A few years ago I helped with a study that was funded by the Canadian Mortgage and Housing Corporation (CMHC) to address this issue for sub-slab applications. A few manufacturers were pushing the product really hard to contractors using mis-information. As a result, the CMHC sought out to dispell the myths. I have attached the CMHC summary for the (much longer) report that we provided to them.
As you might expect, the R-value was negligible in our studies which looked at the 1/2" products, and for sub-slab applications the foil offers no benefit because there is no air space. As Michael and Charlie indicated above, I would suspect you would end up with the R-value for still air.
There was also a really great article written in the Energy Design Update publication a number of years ago. I can't seem to find it now, but I can picture the article now. It took up 1/3 third of one of the right pages in that issue. Can anyone help jog my poor memory? ...
I was the author of the article you are thinking about. I can probably cut and paste it here if I do a little digging.
From the September 2003 issue of Energy Design Update:
Foil-Faced Bubble Pack Under Slabs
Builders have successfully used aluminum foil products as attic radiant barriers for decades. Recently, however, several manufacturers of reflective foil have begun promoting the use of foil-faced polyethylene bubble pack as an insulating material under concrete slabs.
Certainly, foil-faced bubble-pack is an effective vapor barrier, as is ordinary 6-mil polyethylene sheeting. But when installed under a slab, does the aluminum foil in these materials contribute in any way to their thermal performance? And is there any justification in referring to these materials as “reflective” insulation products when installed under a slab?
Puffed-Up Performance Claims
Avariety of “sandwich” products using polyethylene bubble pack and aluminum foil have been developed for use under concrete slabs (see Table 2, page 11). These include foil / bubble / bubble products (Astro-Foil Tuff-Stuff), bubble / foil / bubble products (Concrete Barrier rFoil, Fi-Foil Concrete Shield), and foil / bubble / foil products (Ayr-Foil A2V, Reflectix). Moreover, some manufacturers combine aluminum foil with thin layers of flexible closed-cell foam insulation (Insul-Tarp, Slab-Shield).
Some marketers tempt builders with the claim that the performance of these products compares favorably with that of rigid foam insulation. WE International, a distributor of Concrete Barrier rFoil, declares on its Web site, “Concrete Barrier can serve three purposes underneath concrete: R-10 insulation, a vapor barrier and a radon barrier.” The blurb continues, “How does it compare to 2-inch foam board? It works just as well.” Since rFoil is only 5/16-inch thick, the R-10 claim strains credulity.
Similarly, the Insulation Solutions Web site declares that their 3/8-inch-thick product, Insul-Tarp, has an “R-value equivalent” of R-5 to R-10.
When another manufacturer, Innovative Insulation, was contacted for information concerning the R-value of their foil-laminated bubble pack products, Diane Norwood, an account executive for the company, responded by e-mail that their TempShield Double Bubble / Foil product “will give you an R-value of around R-6” when used under concrete.
Manufacturers explain these unlikely R-values by crediting the near-miraculous effects of aluminum foil. When asked about the performance of rFoil, Eric Deckers, director of marketing for WE International, told EDU, “What the product does is reduce radiant energy loss through the slab by reflecting the radiant heat off the foil in the middle of the product. The foil bounces the radiant heat and sends it back up.” The Reflectix Web site similarly claims that their product reduces heat transfer not only by conduction, but also by radiation: “Reflectix placed beneath a concrete slab … reflects radiant heat.”
Some manufacturers claim that aluminum foil acts as a “thermal break.” For example, the Web site of Environmentally Safe Products has the following explanation for the role of aluminum foil in its Slab-Shield product: “This is where the pure aluminum center-leaf comes into effect. It provides an effective thermal break between the foam layers and prevents the slab or heating system from seeking the cold ground below it, thereby allowing the slab to reach temperature sooner and help the system perform more efficiently.”
A few manufacturers concede that their products have a relatively low material R-value, but assert that when installed in a slab assembly, the aluminum foil contributes to a much higher assembly R-value, as would a layer of foil installed next to an air space in a wall or roof assembly. For example, Claude Pascal, technical advisor at Ayr Reflective, provided the following statement concerning Ayr-Foil A2V, his company’s underslab product: “We don’t provide an R-value for the product; we provide an R-value for the installation. Under concrete the total assembly is R-10.”
They Aren’t Reflective
Claims that underslab foil can reflect radiant heat are misleading. In order to be effective, a radiant barrier requires an air space adjacent to the reflective material; if aluminum foil is in direct contact with other materials, it acts as a conductor, not a reflector. According to David Yarbrough, a research engineer and insulation expert at R&D Services in Cookeville, Tennessee, when foil-laminated bubble pack is installed under a slab, it is not a reflective insulation. “The material as it is used under concrete doesn’t meet the definition of a reflective insulation,” says Yarbrough. “It contains a reflective material, that’s true, but it is not really being used in a reflective insulation application. It is not performing like a reflective insulation because there are no significant reflective air spaces.”
Mike Boulding is the president of TVM Building Products, the manufacturer of rFoil. “In our case we claim 57% reflectivity, which means that the product will reflect 57% of the radiant component of heat transfer,” says Boulding. But in the transfer of heat from a slab to the ground below, radiant energy is almost irrelevant. Any radiant heat source in the room above, or any heat source in the concrete itself, transfers its heat to the concrete, at which point the heat transfer mechanism becomes conduction, not radiation. “Under concrete pads there aren’t any air spaces,” says Yarbrough. “The foil or bubble pack is in direct contact with the ground or fill material, so radiant transport is not a big issue. The big issue is the other heat transport mechanism, conduction. And there is no radiation going directly from the warm room through the concrete and hitting the aluminum foil.”
Some manufacturers of foil-laminated bubble pack assert that the air bubbles trapped in the bubble pack adjacent to the foil permit the foil to perform as a reflective insulation. The problem with this claim is that any performance enhancement contributed by the air bubbles adjacent to the foil is already included in the measured R-value of the material. “The aluminum foil could contribute a little bit to the R-value of the material, because it is changing the radiation transport across the air cells,” says Yarbrough. “But that effect is still part of the measured material R-value. Unless there are reflective air spaces adjacent to the material, you won’t get any additional effect from the aluminum foil.” For underslab applications of these products, the much vaunted reflective ability of aluminum foil is irrelevant.
Even the Reflective Insulation Manufacturers Association (RIMA) concedes as much in their technical bulletin, “Reflective Insulation Materials Used Under Concrete Slabs,” which is posted on the Web at http://www.rima.net/pdf_files/TB101-UnderConcreteSlabs.pdf. This bulletin describes the performance of an R-1.1 “reflective insulation material” installed in a concrete floor system. By including the R-values of 5 inches of gravel and 2 inches of concrete, the floor assembly is assigned a total R-value of 1.95. According to the bulletin, “It is important to note that the calculation used to generate the example described above does not include any additional thermal benefit resulting from the aluminum surface(s) of the reflective insulation material. In other words, the reflective insulation material is performing similar to a non-reflective insulation material.” Although the manufacturers of foil-faced bubble pack may not always provide accurate R-values for their products, these values are known. “The bubble pack products have material R-values that have been measured,”
says Yarbrough. “The values tend to range between 1 and 2, depending on the thickness.”
Is an Air Gap Possible?
To justify calling these products reflective insulations, manufacturers propose several mechanisms whereby small air gaps occur, even when the products are installed under four inches of concrete. John Straube, a principal of Balanced Solutions, an energy consulting company in Waterloo, Ontario, asserts that air pockets do exist under concrete. “Partly because of its corrugated surface, this product [rFoil] produces air gaps between it and the earth below,” he says. But Yarbrough doubts that such small air spaces have much effect on thermal performance. “Although there may be some reflective air spaces due to the roughness of the concrete or the adjacent gravel, the effect is small,” he says.
Chuck Hockensmith is a corporate account executive for Environmentally Safe Products, which manufactures Slab-Shield, a product that combines aluminum foil with thin layers of polyethylene foam. “You will hear some manufacturers claim that there is an air space in there,” says Hockensmith. “But when you pour a slab on top, there is no air space—it is impossible to achieve an air space.”
Very little hard data exist on the performance of foil-faced bubble pack installed under slabs. John Straube and his partner, Chris Schumacher, were hired in 2001 by Covertech Fabricating, a manufacturer of foil-faced bubble pack, to conduct tests comparing the performance of their product with 1-inch and 2-inch extruded polystyrene in an underslab application. But after Straube and Schumacher began the test and provided preliminary data to Covertech, the manufacturer pulled the plug on the testing. Covertech’s owner, John Starr, explained: “We stopped the funding when we weren’t getting the results that we wanted to get. So we changed our focus.”
According to Straube, who is also an assistant professor of civil engineering at the University of Waterloo, “All I have so far is data that suggest that it [foil-faced bubble pack] is better than R-1.1 and worse than R-5. I think there isn’t much point to arguing over whether it is R-1.7 or R-2.5. It is not a big deal one way or another. If you are putting in radiant-heated floors you need at least R-5 under a slab. That means you need more than this product provides anyway, so it is questionable whether you should use this product. I recommend our clients install more R-value than this product can provide.”
Radiant Slabs Need R-5 Insulation
Many experts advise against using foil-faced bubble pack under radiant slabs. According to the March 2002 issue of Solplan Review, “Bubble wrap / foil-coated materials have their use, but they must be used within strict conditions. They can be used as part of a wall system, but are not to be used as insulation under concrete floor slabs.” Similarly, the Technical Research Committee of the Canadian Home Builders Association (CHBA) advises, “Foil-faced bubble-wrap type insulation products are designed for use in assemblies that incorporate an air space on the warm side of the insulation.… Unfortunately, overzealous sales representatives push the products for applications where they will not work as claimed. One such case is using bubble wraps under concrete slabs-on-grade. Under the slab these bubble wraps do not provide the insulation value claimed.”
John Fantauzzi, the technical director of the Radiant Panel Association, echoes the warning provided by the CHBA. “I think the information that is out there is not definitive, so it is almost ‘Buyer beware,’” says Fantauzzi. “I have not seen good definitive testing information to justify its use. There are applications where it does work well, but under a slab is a questionable application at this point.”
Not a Bargain
Prices for foil-faced bubble pack products vary widely, ranging from about $0.25 to $1.18 per square foot, with many sources quoting prices of $0.38 to $0.50 per square foot. Since 1-inch thick R-5 extruded polystyrene is readily available for $0.35 per square foot, installers will save little, if any, money by switching from polystyrene to bubble pack. As Straube points out, “I might recommend it if it were half the price of R-5 rigid foam, but if it costs more than R-5 foam then you have to be crazy or stupid to use it.”
"In order to be effective, a radiant barrier requires an air space adjacent to the reflective material;"
While I understand this, how does radiant roof decking work? I'm referring to OSB with reflective foil or paint on the attic side. the foil or even aluminized low-e paint coating on the underside of the decking is directly adhered to the OSB. there is no air space to reflect heat from above (solar). Wouldn't one expect the heat from the hot shingles to conduct straight through the radiant treatment? (similar to described subslab situation). However studies seem to show that with the roof in full sun, the underside of the radiant treated side is cooler. Homeowners in the South also support this, albeit anecdotally. In the winter, there's plenty of air space on the attic side so I get the reflection of heat back to house works fine in that direction.
A radiant barrier isn't about reflectivity. It is about radiation. Just like the name says radiant barriers don't radiate heat. If you put your hand right next to, but not touching a radiant barrier, you can't feel any heat radiating from it. However if you then touch the radiant barrier it will be very hot! In fact a radiant barrier will actually get to a higher temperature than a flat black painted underside of a roof deck. That is because it can't really radiate away the heat it has absorbed from the sun. But that comparative advantage only happens if you don't short circuit the radiation barrier by denying it an air gap.
I should add that the more closely the radiant barrier is coupled to the roof deck above the better it is. That is because the radiant barrier will absorb the heat through conduction (not radiation) but will stop the heat from reradiating or conducting to the attic as long as there is an air gap. As you might have gathered, RBs are only good for heat and not for cold. Any bubbles formed into the material are insignificant to insulate against cold weather and are useless.
Thanks! this is helpful, so if I understand correctly it's no so much about reflecting the heat conducting from the shingle side (unless there was an air gap between the radiant treatment and the OSB), it's about the emissivity (sp?) of the material back out to the attic space. so does aluminum have low emissivity?
in the case of the bubble wraps (or the foam "prodex" equivalent) why doesn't the middle filler count as an air gap?
"in the case of the bubble wraps (or the foam "prodex" equivalent) why doesn't the middle filler count as an air gap?"
I suppose one could look at the bubbles as an air gap but they aren't good ones because they are quilted so they are a very poor air gap. The surface of the bubble is the low emissivity surface so if you touch that surface with another type of insulation you will short circuit the radiation barrier through conductive action. Also, like I said, RBs only work for restraining radiation of heat. You need to also insulate again infiltration of cold. Why would one pay extra for the very small poor quality insulation value of a quilted bubble in an attic when you could just blow in 10-15 inches of cellulose on the attic floor and get 10 times the insulation value of those air bubbles? Just make sure that insulation isn't right up to the RB (like in a flat roof). It doesn't have to be perfectly separated. You probably will have some proximity at the perimeter of gable and hip roofs. That's OK.