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Foamed glass aggregate is a lightweight, cellular construction fill made by heating processed recycled glass with a foaming agent, then cooling, crushing, and screening the resulting material. The process can use recycled bottle glass, but the available producer information describes recycled glass generally—not a feedstock made exclusively from bottles. The recipe, kiln temperature, expansion, and finished specifications vary by manufacturer, so project decisions should use the selected product’s technical data rather than an assumed industry-wide value.
What is foamed glass aggregate?
Foamed glass aggregate is loose, granular material made by turning processed glass into a cellular mass and breaking that mass into particles. It is also called foam glass gravel or foamed glass lightweight aggregate. The cells contain gas, leaving a porous glass structure that can provide low weight and thermal resistance while still functioning as fill. The particles are used in construction assemblies such as subslab insulation, green roofs, load-bearing fill, and some infrastructure work.
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It is not simply crushed glass. Ordinary crushed glass is dense, solid particles; foamed glass aggregate has been expanded during heating to create cells throughout the material. Nor is it the same product as cellular-glass insulation boards. Those are manufactured as blocks and then annealed and cut into boards, as described in FOAMGLAS documentation. Loose aggregate and boards have different formats and applications.
“Made from recycled bottles” is a useful shorthand, but it can overstate what is established. Producers describe recycled glass as feedstock; the sources do not show that every producer uses only bottles, or that every type of bottle glass is suitable. Ask a supplier what recycled-glass feedstock it uses if the source or composition matters to a project.
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How is foamed glass aggregate made?
The broad sequence is glass preparation, mixing with a foaming additive, controlled heating, cooling, and grading. The details are producer-specific: the sources describe different additives, temperatures, expansion ratios, and cooling behavior, so there is no single universal recipe.
- Prepare the glass. Recycled glass is cleaned and reduced to powder or fine particles. Glavel describes cleaning and milling glass into powder. Foamed Glass UK describes removing metal magnetically, drying and cleaning the glass to remove labels and organic residue, and milling it to about 0.03 mm. These are descriptions of their respective production approaches, not a standard specification for every plant.
- Blend in a foaming additive. The prepared glass is mixed with an additive that helps generate gas as the glass is heated and softens. Glavel says its powder is combined with glycerin and sodium silicate; its technical explanation says glycerin off-gases as the glass sinters. Other descriptions refer more generally to a foaming agent. The additive and its role should not be assumed to be identical across manufacturers.
- Heat under a controlled kiln profile. Heat softens and fuses the glass while gas creates cells in the material. Glavel reports kiln heating to 1,600°F. Foamit’s infrastructure guidance describes a process at about 900°C. These figures belong to different producer descriptions and should not be treated as competing readings of one universal setpoint.
- Cool and fracture the cellular mass. As the material cools, it can crack into a cellular glass mass that is suitable for further processing. Glavel describes a slab fracturing quickly from thermal stress after leaving the kiln; Foamed Glass UK describes cracking during cooling. The exact sequence depends on the production process.
- Crush and screen to size. The fractured material is crushed and sorted into particle grades. The finished grading matters because particle size affects how the product fits the intended design and construction method. A project specification should identify the required grade rather than referring only to “foam glass.”
Published expansion descriptions also vary. Foamit’s 2019 guidance says its material expands to almost five times its original size and is approximately 8% glass and 92% air. Foamed Glass UK reports roughly three to four times the starting volume. These are source-specific figures, not universal constants or a measure of the percentage of bottles recycled.
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Foaming changes the glass from a compact solid into a low-density, cellular aggregate. That combination can be useful where a project needs fill that weighs less than conventional mineral aggregate and can also contribute thermal resistance. Glavel describes its product for subslab insulation, green roofs, and load-bearing fill. NJDOT Technology Transfer’s interview discusses foamed glass aggregate in transportation construction and agency testing.
The same material property can matter differently in each assembly. Under a slab, thermal performance and compressive behavior may be central. In a roof build-up, weight and the details of the complete assembly matter. In infrastructure fill, the project’s loading, grading, drainage, and construction requirements need to be considered by the design team. These are not interchangeable applications simply because the aggregate is lightweight. The product’s tested data and the project design govern whether it is suitable.
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Glavel’s technical data sheet says: “These micropores are critical to the material’s insulating properties, moisture resistance, and compressive strength.” That statement describes the role of the micropores in Glavel’s product; it is not a guarantee that every foamed glass product has the same performance. For any application, review the selected manufacturer’s current technical documentation and the design requirements together.
What specifications should a designer or contractor check?
Foamed glass aggregate does not have one set of values that applies to every brand or grade. Compare products on the properties that affect the assembly, and confirm that each value is reported on a comparable basis. For example, a compressive-strength figure tied to a particular compaction level should not be compared casually with a value measured under a different condition.
| Property | Glavel-reported value | Why to check it |
|---|---|---|
| Dry bulk density | 9–10 lb/ft³ | Relevant to estimating the weight of dry placed aggregate. |
| Moist bulk density | 11–12 lb/ft³ | Provides a different weight basis from the dry value; use the basis appropriate to the design and expected conditions. |
| Compressive strength | 115–125 psi at 25% compaction | The stated compaction condition is part of the value and should accompany it in any comparison. |
| Thermal resistance | R-1.7 per inch | Relevant where the aggregate contributes to insulation; confirm how the value applies to the designed layer. |
| Friction angle | 42° | A geotechnical design input; the project engineer should verify suitability for the intended use. |
| Particle size | 1–3 inches | Grading affects placement and the detailed design of the fill layer. |
Values above are reported by Glavel in its February 2026 Technical Data Sheet; they are not industry-wide specifications. Confirm current values, grade, and test basis with the manufacturer before using them in a project. Product specifications are checked November 2026.
At a minimum, a product review should establish the particle-size range and grading, dry and moist bulk density, compressive strength and its compaction basis, thermal resistance, and any geotechnical values needed for the design. Also confirm that the stated data refers to the actual product and grade being supplied. A label such as “recycled glass aggregate” or a general statement about lightweight fill does not substitute for the project’s required data.
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Where is it used—and what should be confirmed before specifying it?
Documented uses or proposed uses include subslab insulation, green roofs, load-bearing fill, and transportation infrastructure. Glavel lists the first three for its product. The NJDOT Technology Transfer interview describes transportation construction use and agency testing, while distinguishing applications that NJDOT had not used at the time of that interview. That account is evidence of a particular agency’s experience, not proof that every transport application is approved or suitable.
Before specifying the aggregate, confirm these project-specific points with the supplier and design team:
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- Product and grading: Get the precise product name and particle-size grade, not just a generic material description.
- Design values and test basis: Obtain the current technical sheet and verify density, strength, thermal resistance, and other required figures, including the conditions under which they were measured.
- Supply and delivery: Confirm the available manufacturer and grade in the project’s region, supply quantities, and delivery arrangements. Foamed glass aggregate is generally a bulk construction material, so availability and logistics are practical design considerations.
- Installation details: Coordinate placement and any required compaction or other construction procedures with the manufacturer’s documentation and project specifications. Do not infer a field procedure from a laboratory value alone.
- Design review: Have the project’s qualified design professional evaluate whether the particular product satisfies the structural, thermal, geotechnical, and assembly requirements.
These checks prevent a common specification error: transferring a value from one product, grade, or test condition to a different material and assuming it will perform the same way. Producer literature is useful for screening a candidate, but final suitability is a project-design question.
How does it differ from other recycled-glass products?
“Glass aggregate” can refer to several materials with different shapes and uses. Foamed glass aggregate is the loose, expanded, cellular gravel described here. Cellular-glass insulation boards are block-derived products cut into board form, while PORAVER is expanded glass granulate, a related but distinct product format. A project should specify the format and intended function, not rely on the word “glass” alone.
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The distinction matters when comparing performance documents. A board’s data applies to that board product and assembly; it does not automatically characterize loose aggregate. Likewise, a granulate product should not be treated as equivalent to a coarser foam-glass gravel. Compare the specific product’s grading, density, strength, thermal data, and intended applications against the project requirements.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What should readers take away about the manufacturing process?
Recycled glass is prepared, mixed with a foaming additive, heated until it softens and develops gas-filled cells, cooled until it fractures, then crushed and screened into construction grades. That sequence explains how a hard glass feedstock becomes lightweight granular fill. But the recipe and operating conditions are manufacturer-specific: the cited sources report different heating figures, expansion descriptions, and process details.
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For a building or infrastructure project, the most useful next step is not to assume a universal “foam glass” specification. Identify the application, obtain the selected supplier’s current technical data for the exact grade, and have the project team check it against the design. And if recycled-bottle content is a requirement, verify the feedstock with the producer rather than assuming every product is made exclusively from bottles.
Frequently Asked Questions
Is foamed glass aggregate made from every kind of recycled glass?
The cited production descriptions establish recycled glass as feedstock, but do not establish that every glass type is accepted by every manufacturer. If feedstock composition or recycled-content reporting is part of procurement, ask the producer for documentation covering the specific product.
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Can foamed glass aggregate be used in road or transportation projects?
It has been discussed and used in transportation construction, including in an NJDOT Technology Transfer interview. That does not establish blanket approval for a road project; the agency requirements, product data, and project design still determine acceptability.
Does the aggregate’s air content tell me how much recycled glass it contains?
No. Foamit’s approximately 8% glass and 92% air description refers to the composition of its expanded material, not the fraction of recycled input or the share of bottles diverted from waste. Request a separate recycled-content statement if that figure matters.
Is foam glass gravel the same as expanded glass granulate?
They are related recycled-glass products, but names can refer to different product formats and grading. Check the manufacturer’s product description and technical sheet to confirm that the material is loose aggregate suitable for the intended assembly.
