Blog Post

Foamglas – My New Favorite Insulation Material

Foamglas is an inorganic, high-compressive-strength insulation with no need for flame retardants or other hazardous chemicals.

Foamglas is an inorganic, high-compressive-strength insulation with no need for flame retardants or other hazardous chemicals.

Photo: Pittsburgh Corning.
I have a new favorite insulation material. 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, I think he's going to make that happen. I met Rebel at the Building Science Corporation Westford Symposium (a.k.a. Summer Camp) a few weeks ago, and I've been getting more excited about the product ever since.

What is Foamglas?

Foamglas is a cellular glass insulation material that's impervious to moisture, inert, 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. The high compressive strength makes it particularly appropriate for roof decks, green roofs, and parking decks. It is produced in 18" x 24" dimensions in thicknesses from 1-1/2" to 6" in 1/2" increments.

Use of Foamglas as exterior foundation insulation.

Photo: Pittsburgh Corning.
Relative to composition, 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 is in Europe.) 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 creates the insulating bubbles in the Foamglas. CO2 accounts for more than 99% of the gas in the cellular spaces.

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 in the process. You don't want to breathe a lot of hydrogen sulfide, but 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 will know that I've been critical of certain insulation materials for the flame retardants, blowing agents, formaldehyde, and other chemicals in most insulation materials.


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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 (XPS) currently dominates the market. It's better than XPS, because, in addition to the absence of those chemicals, Foamglas is totally impervious to moisture (water and vapor), does not support mold growth, blocks radon, and keeps out termites and rodents. For more on concerns with foam-plastic insulation materials, see my blogs on polystyrene and the global warming potential of insulation materials.

Foamglas being installed for insulating beneath a concrete slab. 

Photo: Pittsburgh Corning.
Cost and availability

Foamglas is more expensive than the other insulation materials we're used to using. 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 that 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, 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 components), 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 is manufactured at two U.S. factories and can be shipped anywhere. Most product is distributed through dozens of dealers that primarily market industrial product. Rebel told me they can even supply it for individual houses--though shipping may increase the cost. With Pittsburgh Corning looking to increase its presence in the building insulation market, and especially in green buildings, this could be a good time to try it out.  

For more information:

Pittsburgh Corning Corp.
Pittsburgh, Pennsylvania

Published September 1, 2010

(2010, September 1). Foamglas – My New Favorite Insulation Material. Retrieved from

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November 9, 2021 - 9:14 am

We don't make or distribute Foamglas; we just write about buidling products.

November 8, 2021 - 3:24 am

I'm interested in using your Foamglas product, do you have an outlet in Australia?

August 3, 2021 - 4:25 pm

Does anyone know if there are companies that can make foam glass panels based on a design I would provide.  Not the standard flat panels but with some design differences.
Thank you.

August 5, 2018 - 4:32 pm

How can Foamglass be inorganic, when it's made of crushed glass and carbon, when the very definition of inorganic is material that doesn't contain carbon?

May 23, 2016 - 11:27 am

Foamglas is a closed cell product with the individual cells containing >90%  CO2 and <0.1% CO and hydrogen sulfide as manufacturing byproducts. Though the material has other end uses, as in this case, it is typically used in high-temperature insulation applications, so, no, fire/gases should not be a concern. Any slow gas release from a fire would be primarily CO2. The concentrations of H2S are simply too low to cause explosion or inhalation concerns. You don't want to be breathing high levels of H2S, of course, but our bodies (and any other anaerobic digestion, including poor composting) produce a bit of H2S anyway and we can process low levels of it without health issues. If you are breathing fumes from a fire hot enough to melt foamglas, then emissions from the insulation are the least of your concerns.

This is a bit of a moot point, however. Though we were hoping for wider distribution, the company is no longer marketing foamglass for general insulation purposes.

September 7, 2010 - 4:36 am

I look forward to the full product review but some questions that come to mind -
How is this product fastened to various substrates?
When used as insulation outboard a wall or roof deck how do you fasten through the Foamglas?
How are the seams dealt with to form a continuous thermal layer?
Can you cut this product on site?

May 10, 2012 - 1:53 pm

Yes, you can cut on site, with a hand saw.  We use various methods to adhere to substrates dependent on application, contact me for more details

May 21, 2016 - 4:33 pm

How does foamglas hold up to high heat, as in house fires? How do the known properties of H2S react in these conditions?

September 21, 2010 - 7:11 pm

Alex, the physical properties/attributes of this product seem to be very similar to Roxul, save for perhaps the compressive strength. However, the pricing and availability seem to be hurdles when compared against a product like Roxul. Also, it's virgin content (for the NA market anyway) vs. recycled stone and slag. What is that gives this the "new favorite" nod in your mind vs. a product such as Roxul?

September 13, 2010 - 10:28 am

Thanks for bring this to our attention. Foamglassl looks very similar to Tremco's Warm-N-Dri which is used in the Tuff N Dri waterproofing system. Both have very low r values. The Warm-N-Dri's major purpose is to move water quickly down the wall to a drain tile and of course it protects the water proofing sealant from being damaged during backfilling.

Will the Foamglas provide a conduit as the Warm N Dri does? Also how is it fastened. i can tell you that the fasteners used to install the Warm N Dri were not good.

October 1, 2010 - 11:06 am

Thanks for your review of the product. At first glance, it does seem a little pricey. However, given the environmental benefits that you have described, it might very well be worthy of paying a little more in the long run. Always good to hear of alternative options.

November 22, 2010 - 4:11 am

Re: Cellular Glass as "green", analysis of the many attributes of various insulation products that define its "green-ness" is complex. Typically, the most important attribute is its insulating efficacy over the life of the product versus its life-cycle cost. Yet issues such as the GWP, ODP, and energy consumption during manufacturing are important. It must also be recognized that intended use of the insulation may be a key factor that can influence its environmental sustainability. For example, some insulations simply do not work well in very humid environments or in underground applications. Far too often, magazine and email articles use "hand waving" analysis that ignore some issues and include only the most positive aspects. I have never seen a credible apples-to-apples comparison of insulation alternatives based on an industry-accepted protocol (e.g. ISO 14000, GaBi or SimaPro software, etc.). Does anyone know of any such objective comparison?

May 10, 2012 - 1:50 pm

We have EN ISO 14001 as well as UL 263, UL 723, UL 790, UL 1256 and NY 07200-89021-2013

November 25, 2010 - 10:30 am

Could Foamglas be use as an exterior finished siding material? Is there any information on its long term exposure to the weather? It would be very usefull as an exterior cladding for a modern style house.

May 10, 2012 - 1:38 pm

Hi there,

Not sure if you ever got this question answered as I am new to FOAMGLAS but the answer is that you can and we have. 

Here is a link to the article about a Passive House project completed in Westport, CT which used FOAMGLAS as the exterior facade.  It was sealed with a pittcoat to add stability and strength as well as seal the joints and act as further waterproof and vapor barrier.  Architect Ken Levinson, PH Consultant Greg Duncan