Foamglas – My New Favorite Insulation Material
An old insulation material, Foamglas, is back and offers some significant environmental and performance benefits over the insulation materials most commonly used below-grade.
I spend a lot of time studying insulation--which is one of the most important components of any green home or commercial building. I have a new favorite. Foamglas® building insulation has been made by Pittsburgh Corning for many decades and is widely used in Europe. For the past decade or two, however, it has only been actively marketed in North America for industrial applications. (It’s been listed in our GreenSpec Directory as an industrial insulation material for years.)
Now Foamglas is back. Axel Rebel was brought over from Europe a couple years ago to rekindle interest in the product for building insulation. As Pittsburgh Corning’s vice president and general manager of the North American Building Division, he’s likely to make that happen. I met Rebel at the Building Science Corporation Westford Symposium (a.k.a. Summer Camp) last month, and I’ve been getting more excited about the product since then, as I’ve studied the particulars.
What is Foamglas?
Foamglas is a cellular glass insulation material that’s impervious to moisture, totally inert (no offgassing), resistant to insects and vermin, strong, and reasonably well-insulating (R-3.44 per inch). It can be used for insulating roofs, walls, and below-grade applications, including beneath slabs. It is produced in 18" x 24" dimensions, and in 1-1/2" to 6" thicknesses, in 1/2" increments. An asphalt-based sealant is used between the insulation boards during installation.
Foamglas is 100% glass—manufactured primarily from sand, limestone, and soda ash. (Virgin ingredients are used in the two North American factories—in Texas and Missouri—while up to 66% recycled glass could be used, and European product has significant recycled content.) These ingredients are melted into molten glass, which is cooled and crushed into a fine powder. The powdered glass is poured into molds and heated (below the melting point) in a “sintering” process that causes the particles to adhere to one another. Next, a small amount of finely ground carbon-black is added, and the material is heated in a “cellulation” process. Here, the carbon reacts with oxygen, creating carbon dioxide, which forms the insulating bubbles in the Foamglas. CO2 accounts for more than 99% of the gas in the cellular spaces, and it is permanently trapped there.
If you scratch a piece of Foamglas (your fingernail can cut into it), you will detect a slight rotten-egg smell from hydrogen sulfide. Iron sulfate is used in the manufacturing process, and a small amount of hydrogen sulfide is produced. You don’t want to breathe a lot of hydrogen sulfide, but there’s very little in Foamglas and it’s locked tightly into the cellular glass—in fact, even after 30 years in place, scratching Foamglas produces the same smell. “It’s proof that the cells are absolutely airtight,” Rebel told me.
I’m working on an in-depth product review for the October issue of Environmental Building News that will address the various performance properties and environmental attributes of Foamglas; I only touch on them here. Readers of my articles and blogs over the last few years know that I’ve been critical of certain insulation materials for the flame retardants, blowing agents, formaldehydeChemical found in many building products; most binders used for manufactured wood products are formaldehyde compounds. Reclassified by the United Nations International Agency for Research on Cancer (IARC) in 2004 as a “known human carcinogen.", and other chemicals contained in them. This is where Foamglas excels. There are no blowing agents that deplete ozone or contribute to global warming. There are no flame retardants or other additives needed to improve fire resistance.
As a 100% inorganic material, Foamglas is inert and fireproof. And it has enough compressive strength to be used under any concrete slab—an application where extruded polystyrene (XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation.) currently dominates the market. It’s better than XPS, because, in addition to the absence of those chemicals, Foamglas is totally impervious to moisture (vapor and liquid), does not support mold growth, blocks radonColorless, odorless, short-lived radioactive gas that can seep into homes and result in lung cancer risk. Radon and its decay products emit cancer-causing alpha, beta, and gamma particles., and keeps out termites and rodents.
Cost and availability
Foamglas is significantly more expensive than the other insulation materials we use. The typical cost of Foamglas T4+ (the most common product for building insulation) is about $1.00 per board-foot, according to Rebel—roughly two-and-a-half times the cost of extruded polystyrene (XPS), which averages about $0.40 per board-foot. Rebel admits that if you’re comparing insulation materials simply based on cost and insulation value, you’re not going to choose Foamglas. “We have to add another value,” he told me. That value can come from replacing other layers in the construction system (vapor retarders, moisture barriers, radon-control layers), from greater durability, from environmental attributes, and even from installing a thinner concrete slab. “We can reduce the thickness of the concrete slab, because Foamglas is so rigid,” Rebel said. Foamglas becomes more cost-competitive if you factor in all of these issues.
Foamglas is manufactured at two U.S. factories (in Texas and Missouri) and can be shipped anywhere. Product is currently distributed through dozens of dealers that primarily market industrial Foamglas materials. Rebel told me that it’s no problem to supply it for individual houses—though shipping may increase the cost and result in some delay. With Pittsburgh Corning looking to increase its presence in the building insulation market, and especially in green building, this could be a good time to try it out.
For more information, contact Pittsburgh Corning Corp. at 724-327-6100 or visit the company’s U.S. website.
In addition to this Energy Solutions blog, Alex writes the weekly blog on BuildingGreen.com: Alex’s Cool Product of the Week, which profiles an interesting new green building product each week. You can sign up to receive notices of these blogs by e-mail—enter your e-mail address in the upper right corner of any blog page.
- Pittsburgh Corning Corp.
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