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Green Building News

Two Startups Seek to Grow Interest in Foam Glass Fill

Foam glass aggregate made an attractive alternative to polystyrene backfill on road and bridge projects. Two Northeast companies see a bright future for the product in residential construction. (Image credit: AeroAggregates)

Two companies in the Northeast are seeking to expand the market for a lightweight, insulating fill made from recycled glass that can take the place of stone aggregate in several residential applications, including subslab fill.

AeroAggregates of Eddystone, Pennsylvania, announced this week it has  opened a second kiln as it increases production of the foamed glass aggregate it now sells in parts of the Northeast. The material is made of post-consumer recycled glass and a foaming agent and, according to the manufacturer, can act as both a drainage and insulating layer.

In Vermont, Burlington-based Glavel is currently importing foamed glass from a German manufacturer but plans to open a 12,000-square-foot plant in St. Albans, Vermont, next year as it sees increased demand ahead.

In a telephone call, AeroAggregates CEO Archie Filshill said that he and a colleague were introduced to the technology in Norway six or seven years ago. After a round of testing in 2016, AeroAggregates began producing foamed glass in 2017 and now distributes it in an area from Massachusetts south to Virginia Beach and west to Pittsburgh.

One of its chief uses is as a replacement for the Styrofoam used for soil reinforcement, stabilization and backfill in infrastructure work — highway, rail and bridge projects. Interest among state transportation officials grew when they realized the material, unlike polystyrene, wasn’t flammable and wouldn’t melt when exposed to gas or diesel fuel, Filshill said.

Later, Filshill saw potential value in the use of foamed glass as backfill on construction sites. Because it’s lighter than stone, it’s easier and less expensive to transport, and it can be used as a replacement for the rigid foam and crushed stone that’s now used under concrete slabs by many builders.

“It’s acting as a drainage layer, a capillary break, and as an insulating later,” he said.

Among its biggest customers are New York City contractors who specialize in green roof systems, Filshill said. Foamed glass is 80% to 90% lighter than stone aggregate — between 10 lb. and 20 lb. a cubic foot — and can be placed on a 1:12 roof slope without any reinforcement.

In residential construction, Filshill said, builders who are now using rigid polystyrene insulation and crushed stone under slabs could switch to foamed glass for about the same cost.

“This gets placed like gravel so you replace your gravel layer with this and that would also act as your insulation layer. So you’re getting a two for one replacement. It’s easily put in, and there’s no waste.”

Filshill said the insulating value of 12 inches of foamed glass ranges from R-11.5 to R-15.7. Costs run between $70 and $80 per cubic yard.

“There is also a slight savings on installation,” he added, “because the material just gets dropped and plate-tamped, which you’re going to have to do with your stone base anyway.”

Filshill said foamed glass also could be used as backfill around foundation walls, and as a free-draining fill behind retaining walls and under patios.

Recycled glass mixed with a foaming agent and heated to 1,800°F becomes a lightweight, insulating material that can used in a variety of construction applications. (Image credit: AeroAggregates)

Foamed glass is manufactured in a gas-fired kiln under license from its European developer. Powdered glass is mixed with a foaming agent and when heated to 1,800°F the soft glass becomes infused with bubbles. Although the kiln is gas-fired, Filshill said, foamed glass has half the carbon footprint of polystyrene and expanded shale, another lightweight aggregate option.

Welcomed by advocates of foam-free construction

Glavel’s website lists many of the same benefits as AeroAggregates, including high compressive strength, light weight, low thermal conductivity, and cost effectiveness.

Company CEO Rob Conboy said Glavel grew out of a Passive House conference he attended in Germany in 2016. He was scouting for European technology that could be used to lower the cost of energy-efficient construction in the U.S.

Foam glass is used extensively there, he said, but is not widely known in North America. But interest has been strong among builders who are looking for foam-free products.

“We’ve got some fairly good sized roof projects as well as some folks who are foam-free practitioners looking to use the product,” he said. “We’ve had multiple conversations in multiple channels about how do they look to standardize foam glass gravel in their construction specifications.”

Glavel sells for between $85 and $100 per cubic yard on the east coast (orders have gone as far as Seattle). When you calculate the installed cost of XPS or EPS with labor and gravel, Conboy said, “we are very cost-competitive and in some cases we might be cheaper.”

When compacted to about two-thirds of its original loose depth, the insulating value of foam glass aggregate reaches about R-1.7 per inch, according to its Vermont importer. (Image credit: Glavel)

Compaction is key to performance. The material offers thermal performance of R-1.7 per inch, but only after it has been compacted by about one-third. So, Conboy said, a subslab layer performing at R-10 (equal to 2 inches of XPS) would require between 9 and 10 inches of loose glass foam that would be mechanically compact on site.

Glavel’s two production lines will use some 15,000 to 17,000 tons of recycled glass to produce 140,000 cubic yards of foam glass per year.

“We think there’s a bright future for foam glass gravel,” he said. “We love the fact that we’re going to be taking something of little or no value and turning it into a product that’s good for the planet and an amazing alternative to a petroleum-based product that’s laden with lots of chemicals, and do some good.”

Talking with potential retail partners

Both AeroAggregates and Glavel are of interest to 475 High Performance Building Supply, a New York-based retailer specializing in foam-free building products.

“We’re very bullish on it in the long term,” said Chief Operating Officer Ken Levenson. “We think it’s a win-win-win once you’ve got the supply chain and the manufacturing together. You’re taking recycled glass and upcycling it into an insulation product for buildings. It’s one of the few products that has this magical, virtuous cycle — how we can build and not just minimize our impact but have a positive impact.”

Foam glass is especially interesting because it serves two purposes — drainage and insulation — and that ultimately simplifies the construction process, he said.

“The big issue obviously is cost, and that’s really about having demand at scale and production that’s local,” Levenson said. “It’s not like you can just build a factory in Indiana and ship it all over the country and compete.”

The company has been talking with both AeroAggregates and Glavel and trying to help them introduce foam glass to more potential customers. But for now, 475 isn’t listing the product on its website.

“It’s a product we want to support and see how we can help it grow,” Levenson said.


  1. Expert Member
    Malcolm Taylor | | #1

    I hope this works out and becomes widespread. The glass we recycle here gets landfilled anyway because there is no demand.

    I'm not sure I'd be comfortable working with a substrate I had to compact by 1/3rd to get adequate insulating value and good bearing. That's a huge amount.

    1. Peter L | | #2

      Good point. Plus I don't want to be the guy operating the vibrating compactor for hours and hours to get it to 1/3 compaction.

  2. Jaccen | | #3

    Could this be used as free draining, residential house backfill? It seems that would be an easy to way to place exterior insulation on the basement walls. Even if its performance was degraded without 1/3 compaction (ie. say R-1 instead of R-1.7 due to subpar compaction), that's still significantly better than soil. It would also be useful for insulating sewer mains lacking frost cover.

  3. Expert Member
    Malcolm Taylor | | #4

    The biggest obstacle, as they point out, is that it is a manufactured product. All the fill and aggregate that goes into one of my builds comes from pits within ten miles - and even then the trucking is a large part of the expense. Getting this stuff from where it's made to where it's needed is a problem.

    1. Charlie Sullivan | | #7

      You could imagine a scenario in which there are small plants scattered as widely as gravel pits and recycling centers are now, leading to similar distance trucking with lower fuel consumption. And to the extent that this replaces foam as well as gravel, the distance the foam is trucked is typically pretty long. So in that sense, the obstacle is getting the usage up to the point that it becomes common enough to approach that scenario.

  4. User avater Expert Member
    Dana Dorsett | | #5

    I'm curious to know what they're using as a foaming agent for this glass. Anybody know the nature or chemical classification of those agents?

  5. Charlie Sullivan | | #6

    I don't know about these particular materials, but I found an article that generally describes the options in two paragraphs quoted below; in summary it's probably CO2 from burning some carbon added to the mix.

    "It is generally accepted that foaming agents are of two types: neutralization and redox agents. The first group in-cludes salts (as a rule, carbonates), which in heating decompose with emission of gases (CO2). Intense gas release during their decomposition breaks the walls of individual pores, which merge and create a maze-like system of cavities in glass. Such foam glass has high water absorption and elevated soundproof parameters.

    "Redox gas-forming agents are used to produce heat-insulating foam glass, i.e., a material in which sealed pores prevail. Such gas-forming agents are carbon-containing materials: coke, anthracite, soot, graphite, less frequently silicon carbide. The reason for gas emission in these materials is the reaction of oxidation of the foaming agent by gases dissolved in the glass melt. Such gases are primarily oxygen and sulfuric anhydride."

    That's from Spiridonov, Y.A. & Orlova, L.A. Glass and Ceramics (2003) 60: 313.

    Also, it's a lot like foamglas, and they have a page that describes adding carbon powder added before it goes in the furnace. Foamglas does clearly state that no HFCs, CFCs, or HCFCs are used on another page.

  6. Charlie Sullivan | | #8

    For a while, Foamglas was available for building insulation in the US, in board form. It was rapidly becoming a favorite replacement for foam: insect-proof, low GWP, non-flammable, no toxic flame retardants added, waterproof, high compression strength ... Then Owens Corning dropped it as a building material in the US--it's now sold in other countries for building insulation and in the US for industrial use only.

    This seems like the same concept, but broken into bits as it comes off the line. I can see how there are some applications where the crushed format is useful, but I would think that boards would be preferable for insulation applications, having higher R-value per inch and not needing compaction to get there. I hope that some of the makers of this stuff can tweak their lines and sell boards as well.

    It seems like it has good potential to work for a FPSF (frost protected shallow foundation), either in the crushed format or the board format. But I do wonder about the long term properties in that sort of application. For example if silt gradually washes in and fills between the grains, will that reduce the R-value? The wouldn't happen under a slab, but it might for perimeter insulation.

  7. Vince Caruso | | #9

    Love to see this used under Porous Parking Lots and Porous Roadways, makes a great idea even better with recycled glass. Looks like a great product all the way around.
    Folks like the guy with the plate compactor on this stuff need a mask to avoid Silicosis, which is a fibronodular lung disease caused by inhalation of dust containing crystalline silica.

  8. User avater
    Kent Thompson | | #10

    Relatedly, I'm planning on using lava rock as my under slab drainage layer. Here on the west coast it's cheap and readily available from rock yards. Our lava rock is mined from Northern California from what I understand. It's R value is around 1.5. Pumice is also available here too but more expensive and potentially less compactable. One advantage of these naturally 'foamed' stones is that presumably they have a lower embodied carbon depending on shipping distances.

    This seems like a cool product...fancy lava rock!

  9. Afilshill | | #11

    A lot of great comments and questions. There are several types of foamed glass based on various production methods.
    AeroAggregrates website contains more detail and a technical library for additional information. Feel free to email technical questions to [email protected]

  10. User avater
    Jon R | | #12

    Looking only at R value, I calculate EPS to be 1/3 the cost.

    1. Michael Horgan | | #13

      At material face-value alone, maybe. But with this, you can remove the cost of cu. yd. for gravel sub-slab, remove the cost of purchasing and laying two layers of rigid foam board. The compaction of aggregate will be part of any install, so that labor aspect stays no matter the material.

      On a current project in California, we have $3000 worth of gravel being delivered to the site and another $2500 in sub-slab foam and install. The cost for Glavel delivered to the jobsite will be $3700.

      Aggregate and foam-free R7 in one shot for $3700? Yes, please.

      (Wrote wrong number there first time! Fixed it!)

      1. Afilshill | | #14

        Mike, Aero Aggregates is currently shipping several projects to California from Philadelphia if you are interested.

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