Definitive Foam Glass Aggregate Guide

What is Foam Glass?

Foam glass can go by a multitude of names; foamed glass aggregate, foam glass gravel, or cellular glass. Whatever terminology is used, it’s a lightweight, thermally insulating aggregate made entirely from post-consumer recycled glass. Whether it’s being employed as structural fill for civil infrastructure projects, as thermal insulation underneath a commercial or residential slab, or even as lightweight green roof fill, foam glass is an ideal building material to solve some of the construction industry’s most pervasive issues. Since foam glass is derived entirely from recycled glass, it’s embodied carbon is incredibly low (stay tuned for our EPD and LCA in 2022), making it one of the greenest building materials on the market. 

History of Foam Glass

The discovery of foam glass was in the early 20th century by a Soviet scientist, but the material did not generate demand until later in the 20th century. High performance buildings and carbon footprint awareness were both catalysts for the increased popularity of foam glass.

Foam glass made in the early 20th century was annealed into blocks and made using virgin glass. It wasn’t until the turn of the century that manufacturers in Europe began using recycled glass and eliminating the annealing process from their operations. Instead, they allowed the thermal stress associated with cooling upon exiting kilns to naturally break up the foam glass slab into aggregate. These shifts decreased the product’s embodied carbon and manufacturing simplicity, while increasing the breadth of foam glass applications. 

Around the same time that European foam glass manufacturers were making shifts to recycled glass and aggregate, recycling was a burgeoning industry. The pairing of surpluses of recycled glass with increased demand for recycled glass cullet for use in foam glass created a market synthesis resulting in a foam glass boom. Manufacturing facilities popped up all over, from Scandinavia, to Germany, Austria, and more. With the use of recycled glass dropping the embodied carbon of foam glass, it quickly became coupled with high performance buildings, whose need for uncompromising performance and material sourcing was a top priority.

Fast forward to 2022, foam glass is a fully mature industry in Europe, where use is ubiquitous and done across many construction verticals. Foam glass is beginning to blossom in North America, where Glavel is a leader in low embodied carbon foam glass.

Physical Characteristics

Load bearing – 116 psi compressive strength at 10% deformation, post compaction

High friction angle – Pieces allow for mounds up to 45° slopes

Frost heave resistant – Will prevent cycles of freeze and thaw

Produced from recycled glass – Categorized as ‘clean fill’

Water resistant – Closed cell structure facilitates runoff

Non combustible – Will not burn, nor propagate fires

Inert – Prevents rodents, termites, bacteria, and rot

Thermal insulation – R1.7 per compacted inch

Self interlocking – Distributes loads evenly

Lightweight – 9.8 pounds per cubic foot

Closed cell – Acts as a drainage layer


Production begins with post-consumer recycled glass. Glass of all colors is cleaned to <1% non-glass to eliminate any paper, plastic, ceramic, or other contaminants that may alter the consistency of foam glass manufacturing. It’s possible to use glass that is cleaned to <5% impurity, but the final product does not come out as high quality as its <1% counterpart. The cleaned, recycled glass is then sent through a ball mill, where it’s ground into an incredibly fine powder to then be mixed with a foaming agent. A variety of foaming agents can be used, depending on the manufacturing method being employed; but the purpose of the foaming agent is to create a reaction in the glass powder once it makes its way into the kiln. 

Upon being mixed with the foaming agent, the mixture is laid 2cm thick onto a chain mesh belt, which moves slowly through a kiln with a specific thermal profile to slowly heat the glass to 1,500º. As the glass and foaming agent hit that temperature, the glass softens, and chemical reactions cause the mixture. to foam up and create closed cell micropores.

Upon exiting the kiln, the foam glass slab is 8cm, 4x the original thickness. The final 17m on the road to turning recycled glass into foam glass is the cooling table. During this cooling process, the foam glass slab is exposed to temperatures much colder than the kiln, causing shock and thermal stress, which naturally breaks up the slab into aggregate sized pieces. At the far end of the cooling table, the pieces fall off onto a conveyor belt, where they’ll be sent to bagging or immediately to shipping. 

Glavel cooling table

Foam Glass Applications

Sub Slab Insulation

As a sub slab insulator, foam glass can be used to thermally insulate beneath a concrete slab while also acting as a drainage layer. With its compressive strength of 116 psi at 10% deformation (post compaction), it can be used beneath structural footings as well as on the exterior of a stem wall for additional insulation. In use for both commercial and residential applications, foam glass can replace rigid foam board and crushed stone aggregate.

Green Roof Fill

Weighing only 9.8 pounds per cubic foot, foam glass is 90% lighter than traditional gravel aggregate fill. A foam glass roof installation reduces building strain and increases the ability to build creative landscapes. Foam glass is also highly frictional, when compacted it can be angled in slopes up to 45°. This gives landscape architects the ability to introduce slope and creativity into designs. 

Civil / Infrastructure

As a structural fill, foam glass aggregate can address many of the challenges that the infrastructure world faces today. Whether that is decreasing structural loads, reducing lateral earth pressure, or stabilizing embankments, foam glass can be a solution to a variety of the civil world’s problems. 

Example Commercial Installation