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How to Make Foamed Glass

Foamed glass insulation has a wide range of industrial uses.
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Foamed glass is a highly effective and versatile industrial insulating material made primarily from recycled glass. Foamed glass is manufactured using a process that traps gas bubbles in the glass, creating an expanded material with a spongy consistency. Also known as foamed glass grain or cellular glass, foamed glass is lightweight and has fine, watertight pores that make it an exceptional barrier against moisture, humidity and debris. Materials for making foamed glass can be obtained from foamed glass manufacturing and supply companies.

Things You'll Need:

  • Crushed glass
  • Powdered cullet
  • Coal powder
  • Industrial glass crusher
  • Kiln forms
  • Tunnel furnace
  • Protective clothing
  • Glass-cutting saw

Clean and crush recycled glass material using an industrial glass crusher. For time and cost efficiency, use enough glass to fill the glass furnace to capacity. For best results, use glass that has a similar expansion coefficiency, the temperatures at which the glass melts and re-solidifies.

Mix crushed glass with powdered cullet, a waste-glass material similar to sand that adds strength to the glass, and with a carbon-based material such as coal powder. The carbon additive reacts with the glass to create carbon dioxide, which in turn helps develop a foam consistency with a volume approximately 15 times that of the original crushed glass.

Place the crushed-glass mixture on heat-tolerant kiln forms that have been pre-treated with an anti-sticking agent, such as kaolin or an industrial-strength, silica-based kiln wash.

Load the kiln forms onto the roller conveyor of an industrial trolley attached to a high-temperature tunnel furnace. The glass should be heated to the melting point, typically 1,000 to 1,300 degrees Celsius.

Slowly cool, or anneal, the foamed glass. Gases escape during heating, allowing the glass to expand and then stabilize during cooling. The finished product resembles pumice stone.

Saw the cooled foamed glass into bricks.


The volumes of crushed glass, cullet and coal powder, and their ratios to one another, are based on the density of the foamed glass being created. Different densities are used for different insulating projects. High-density foamed glass has smaller pores than low-density foamed glass does. Higher-density glass is therefore stronger and is used for such purposes as insulating structural walls in buildings. Low-density foamed glass is typically used for purposes such as insulating windows.


  • Wear protective clothing and eye wear during all phases of making foamed glass. The annealing, or cooling stage is vital to the stability of the finished product. Foamed glass that cools too quickly is subject to internal stress cracks.
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