Cellular glass (Foamglas)

Cellular glass — in Danish skumglas or celleglas — is a rigid insulation material built from millions of small, closed glass cells.

The material is produced in three steps:

1. Raw glass (in the case of Foamglas, mainly recycled glass) is crushed into a fine powder and mixed with a small amount of carbon.
2. The powder is poured into moulds and heated in ovens to approx. 1,000 °C. At that temperature the carbon releases gas, and the glass "foams up" — the material expands roughly 20 times its original volume. [foamglas kompendiet.pdf p.3]
3. The blocks are cooled slowly (annealing), cut and milled into finished boards, pipe sections, segments and special fittings — typically starting from blocks 300 mm thick. [foamglas kompendiet.pdf p.3]

Inside each individual cell there is a tiny amount of hydrogen sulphide (H₂S) — the inert gas that formed when the glass was foamed. This gives Foamglas a characteristic smell when you saw into it. The gas is packed so sparingly and so diluted that it poses no health risk during normal handling, but it explains why you should always saw in a ventilated area. [foamglas kompendiet.pdf p.3]

The result is a 100 % closed-cell material. This is crucial — because the cells are closed (not open as in mineral wool or elastomeric foam), neither water, water vapour nor oil can penetrate. The material is vapour-tight in itself and does not require a separate vapour barrier. [Terostat brochure 2013 p.2]

Foamglas was developed in the 1930s and launched commercially by Pittsburgh Corning in 1942 (a joint venture between PPG Industries and Corning Glass Works). One of the first prestigious applications was insulation during the renovation of the White House in 1952.

The material came to Europe in 1957, and Pittsburgh Corning built their European factory in Tessenderlo, Belgium in 1964 — it still supplies the majority of the Foamglas installed in Scandinavia. In 2017 Owens Corning bought Pittsburgh Corning, so today Foamglas is part of the world's largest insulation group. The product name and specifications are unchanged. [owenscorning.com — 2017 acquisition]

In Danish technical insulation, Foamglas has been used for over 50 years, primarily within the chemical industry, oil and gas (especially the North Sea) as well as district cooling/cryogenic plants — all places where other materials have failed due to moisture, fire or corrosion under insulation. [foamglas kompendiet.pdf p.3]

Cellular glass is the insulation material with the widest application temperature range that exists — from below -260 °C (cryogenic, close to absolute zero at -273,15 °C) up to +430 °C. No other insulation can achieve this in one single material. [foamglas kompendiet.pdf p.3]

Thermal conductivity (λ): Foamglas' λ is not particularly low compared with e.g. PIR (0,022) or aerogel (0,015). The interesting property is that the λ is very stable over time — because no moisture can penetrate, the insulating performance does not deteriorate year after year, as happens for example with mineral wool in outdoor environments or PUR that releases blowing agent. The lambda value is effectively constant throughout the entire service life. [Terostat brochure 2013 p.2]

At very low temperatures (cryogenic) the λ actually improves — at -150 °C it drops all the way down to 0,029 W/(m·K), better than mineral wool can achieve. [foamglas kompendiet.pdf p.6]

Vapour tightness: the μ value is ∞ (infinite). In reality the μ is extremely high — even a small scratch in the surface does not affect the material's vapour tightness, because diffusion occurs cell by cell through millions of closed glass walls. By comparison, EPDM elastomeric foam has a μ value of approx. 10,000, mineral wool around 1, and a plastic vapour barrier perhaps 50,000. [foamglas kompendiet.pdf p.4]

Reaction-to-fire class: A1 according to EN 13501-1 — the best possible class. The material is completely non-combustible (it IS pure glass), contributes no heat release, smoke or flaming droplets, and only melts above 700 °C. This means Foamglas may be used where other insulation is prohibited, e.g. in escape routes, atria, tall buildings and fire-compartment penetrations. [Terostat brochure 2013 p.2]

Compressive strength: Foamglas can bear load — something very few insulation materials can. S3 has 900 kPa (0,9 N/mm²), which means a large man (100 kg) on a shoe sole of 10 × 10 cm puts the material under approx. 100 kPa — only about 1/9 of the ultimate strength. This is why Foamglas can be used as a structural insulating foundation beneath hot pipes, tanks and compressor foundations without either metal supports or thermal bridges. [foamglas kompendiet.pdf p.19]

Water absorption: practically 0 %. Even if a piece of Foamglas is dipped fully in water, it does not absorb the liquid — it is pure, closed glass.

1. Completely vapour-tight — no separate vapour barrier needed. All other cold pipes (chilled water, freezing installations, LNG) must have a carefully installed vapour barrier. With Foamglas the material itself is the vapour barrier — you save a layer, and you avoid the risk of the hole-in-the-foil error that ruins 90 % of cold insulation in practice. [Terostat brochure 2013 p.3]

2. 100 % non-combustible — can be used anywhere. Class A1. Fire contribution = 0. No smoke, no dripping, no flame spread. Especially relevant in offshore environments, refineries, transformer stations and escape routes. [foamglas kompendiet.pdf p.5]

3. Withstands extreme temperatures — at both ends. The only material that works both at -260 °C (LNG, liquid oxygen, liquid nitrogen) and up to +430 °C (superheated steam lines). PIR fails at -50 °C, mineral wool becomes damp and crumbles in a cryogenic environment, elastomeric foam cannot withstand above +110 °C. [foamglas kompendiet.pdf p.3]

4. Bears load — can be used as a structural insulation material. Beneath foundations, tank bottoms, concrete floors in cold rooms. Eliminates thermal bridges through steel supports. [foamglas kompendiet.pdf p.3]

5. Insects, rodents and mould cannot break it down. It is pure glass — no organic nutrition. The pests literally have nothing to go after. This is also why it is popular in the food industry. [foamglas kompendiet.pdf p.3]

6. Chemically resistant. Resistant to almost all oils, acids, organic solvents and their vapours. Only broken down by hydrofluoric acid (hydrogen fluoride) and hot concentrated alkaline lye — rarely a problem in technical insulation. [foamglas kompendiet.pdf p.3]

7. Prevents Corrosion Under Insulation (CUI). The single largest cause of damage in the petrochemical industry is corrosion under the insulation, where moisture is trapped between pipe and insulation. Foamglas' combination of 0 % water absorption and full vapour tightness eliminates that problem — which is why it is required by among others the NORSOK standard for offshore installations up to +180 °C. [Terostat brochure 2013 p.10] [foamglas.com / Statoil NORSOK application]