Insulation Materials: Cellular Glass

Allen Dickey

Allen Dickey is a Senior Product Manager of Pipe and Equipment Insulation Systems for Pittsburgh Corning and a NIA-certified insulation energy appraiser. He has more than 28 years in the insulation industry. He holds a B.S. in Chemistry from the University of Pittsburgh. He can be contacted at

Steve Oslica

February 1, 2008


Cellular glass insulation was developed more than 60 years ago. It is believed to have been a modification of technology that existed in Europe at the time. It was discovered that by making glass, then destroying it and baking the glass powder (with certain additions to the batch), a cellular glass “bun” could be created.

The beauty of the bun was that it was 100-percent glass with insulating and flotation properties. The glass composition made it moisture, high heat, and fire resistant. The cellular nature of the glass provided insulation and flotation. Thus, the search for new end-use applications began.

One of the first such end uses was in flotation blocks for submarine nets in U.S. harbors during the latter days of World War II. At the time, cork was in short supply and it was discovered that the cellular glass would remain buoyant and continue to hold up the nets, even after being split up by gunfire, which would originate from submarine surface guns.

At the time, cork was also used as an insulation in cold storage facilities. Because of the moisture resistance of cellular glass, it was a natural fit for cold storage or cold process service, because the vapor drive from ambient air to a cold surface creates great potential for insulation saturation. This was not a problem for cellular glass, which is resistant to such vapor drive. Thus, from the 1950s to the 1970s, the use of cellular glass in cold storage facilities became common. At this time, cellular glass insulation would also find its way into the below-ambient industrial piping and equipment markets.

As a natural outgrowth from cold storage applications, cellular glass insulation began to be used in commercial roofing. In fact, cellular glass was the first insulation to be manufactured into a “tapered” roof insulation, which enabled conversions of “flat” roofs to “low slope” roofs.

The dimensional and strength properties of cellular glass insulation led to the use of the material in load-bearing applications. Higher density grades of cellular glass insulation were developed and, as a result, today more than 90 percent of liquefied natural gas (LNG) storage tanks worldwide are built on a cellular glass insulation base.

Eventually, with more utility systems being installed underground–direct buried, in trenches, or in tunnels–ground water resistance became a major factor in insulation systems retaining their original thermal properties. It was determined that cellular glass worked well in these installations because of its resistance to water. Jackets and finishes were then developed to ensure that physical damage to the cellular glass would not take place during the backfill process.

Over the years, more end uses have emerged that require high-performance insulation systems using cellular glass. For example, systems that cycle from very low temperatures to very high temperatures create the potential for an insulation’s dimensional instability. Cellular glass is able to withstand these temperature cycles without affecting the product’s dimensional stability. 

New applications for cellular glass insulation have continued to develop. One such application niche involves a growing number of plants that have to deal with flammable liquids as a part of their processes. It has been determined that insulations may “wick” flammables like oil and other chemicals, which can provide an ignition or fuel source in the event of a fire. Because cellular glass insulation is non-combustible and nearly 100-percent closed cell, cellular glass insulation has become the standard product in these applications.

The Manufacturing Process

To manufacture cellular glass, the glass itself must be made. The material is then drawn out of a melter at very high temperatures and allowed to cool. The cooled glass is pulverized to a fine powder, and foaming agents are added. The resulting “ground batch” is measured into pans, which pass through cellulating furnaces at approximately 1,000°C, where the material begins to foam.

The resulting “buns” are removed from the cellulating furnaces and placed into annealing ovens for several hours before finally being transferred to the finishing process. There are multiple steps in the quality assurance processes to ensure that there are no defects in the blocks. After inspection are palletized and shrink-wrapped before being shipped.

Globally, the majority of cellular glass insulation is used in block form. However, for industrial insulation applications, the cellular glass insulation blocks are fabricated to produce pipe insulation, fitting covers, and other special shapes by a distributor or fabricator. ASTM C1639 serves as a guide for fabrication of cellular glass insulation.

Product characteristics of cellular glass include the following (testing certifications available from manufacturers):

  • Moisture Resistant
  • Permeability: 0 Perm in
  • Will Not Wick Flammable Liquids
  • Consistent Insulation Values (No Aging)
  • 100-Percent Glass/No Binder or Fillers  
  • Flame Spread 0/Smoke Developed 0
  • High Compressive Strength
  • Wide Temperature Service Range
  • Dimensionally Stable
  • Non-Combustible

Cellular glass insulation for mechanical insulation applications should be manufactured to comply with American Society for Testing and Materials (ASTM) C 552—Standard Specification for Cellular Glass Thermal Insulation.

Common Applications for Cellular Glass

  • Chilled Water Pipes and Equipment
  • Stainless Steel Hot Water Lines
  • Hot Oil Piping and Equipment
  • LNG Piping
  • Green Roof Insulation
  • Underground Steam Distribution
  • Cold Process Pipes and Equipment
  • LNG Tank Bases
  • Ethylene Plant Pipes and Equipment
  • Fireproof Building Panels

Manufacturers of cellular glass have traditionally participated in important NIA committees, and their technical information can be found in the following locations: the Manufacturers Technical Literature (MTL) Product Catalog at, on the MTL Product Catalog CD, within the National Insulation Training Program (NITP), and in the Midwest Insulation Contractors Association (MICA) Insulation Standards CD. Websites are also a good source for up-to-date technical information about cellular glass.

Figure 1

  1. All properties are for the generic material type and will vary by grade and by manufacturer. All properties should be verified with individual manufacturers. Properties that are not stated may or may not be an indication that a material is not appropriate for applications depending on that property. This should be verified with the specific manufacturer.
  2. Surface burning characteristics are valid for 1-inch thickness; verify results for type and any other thickness with the manufacturer. (Not applicable to cellular glass.)
  3. When a property is out of the specified usage range, it is shown by N/A3. Properties that are not listed or stated are so shown.
  4. All properties listed are for the core insulation material only and may not be indicative of the performance of an insulation system, including vapor retarders, adhesives, and sealants.
  5. Many materials can be used for applications outside of the ranges listed, but additional precautions must be followed. The specific manufacturer should be consulted for detailed recommendations.
  6. Some values, such as specific thermal conductivities at various mean temperatures, may be interpolated value.
  7. This chart has been established for products with current ASTM standards.