What Is Foam Glass Insulation?

Foam glass insulation–also called cellular glass or porous glass–is 100% glass. It can be formed into rigid insulation boards for exterior building applications, pipe insulation, and aggregate that replaces gravel under concrete.

Patented in France in 1932, foam glass insulation has been used extensively in Europe for decades. It is becoming more popular in North America because of its many beneficial properties.

What Is Foam Glass Insulation?

What is Foam Glass?

Foam glass is a mixture of crushed recycled glass and sand and limestone (the raw materials used to make glass), and a blowing agent–such as carbon. The gas in the blowing agent causes the glass to foam–then harden and form tiny closed-cell glass bubbles filled with carbon dioxide.

Its name is derived from the process. There is no residual foam in the finished product. The open interiors of the glass beads account for 80% to 90% of the total product. Glass makes up the balance. This makes for a very strong non-compressible insulation board.

Foam Glass Insulation Uses

Foam glass insulation is used for walls, roofs, and floors. It is ideal for below-grade and under concrete slab applications because it does not absorb moisture and provides a barrier to radon gas. The wall and roofing product is typically 24” long x 18” wide. It is available as 1 ½ “ – 6” thick sheets in ½” increments.

Foam glass is also manufactured as an aggregate to use under concrete slabs and as a backfill to replace gravel covering weeping tile and concrete footings. It can be used to insulate heat ducts and pipes where it reduces heat loss by 25% more than traditional insulations.


  • R-value. Approximately R-3.44 per inch. About the same as fiberglass.
  • Fire. Classified as incombustible according to European standards.
  • Moisture. Waterproof. Will not absorb moisture during its lifetime. Acts as its own vapor barrier. Does not rot.
  • Frost. Very high frost resistance.
  • Pests. Insects and rodents will not eat into glass.
  • Mold. Inorganic glass does not support mold, mildew, or plant life.
  • Compression. Does not compress even under long-term weight and use–such as under flooring and concrete slabs.
  • Stable. Does not expand or contract. Will not have gaps and cracks in the insulation blanket.
  • Installation. Lightweight. Easy to work with. Can be cut with normal construction tools including handsaws. Cannot be nailed or screwed. Adhesive is used to secure it to walls. Grout fills the seams between panels.
  • Green. Eco-friendly insulation uses at least 60% recycled glass. No added chemicals. No off-gassing. Non-toxic.
  • Sound. Reduces noise by an average of 28.3 decibels.


  • Cost. Approximately $1.00 per board foot. Extruded polystyrene insulation is about $0.40 per board foot. (A board foot is one square foot of area that is one inch thick.)
  • Availability. As of this writing, there are only two foam glass manufacturing facilities in the US. They ship throughout the country. Freight costs and minimum quantities may apply.
  • Inflexibility. Must be applied to smooth flat surfaces.
  • Fragility. Can be fragile and brittle. Susceptible to vibration damage.

Foam Glass Insulation in Europe

Foam glass manufacturing facilities are located in Belgium and the Czech Republic among other locations. Germany is the home of Europe’s largest foam glass aggregate manufacturer. Distribution throughout the EU is easier than in the US. Customers are more familiar with the product and eco-friendly insulation products are preferable.