What is Glass Wool Insulation?

Glass wool insulation is another name for fiberglass insulation. It is also called glass fiber insulation and fiberglass segments. Light, easy to work with, and very cost-effective glass wool is used to insulate more houses than any other type of insulation.

What is Glass Wool Insulation?

Glass Wool Production

Glass wool insulation is made by combining recycled glass, limestone, soda ash, and sand. The mixture is heated to 1450 degrees Celsius; then forced through a fine mesh to create fibers resembling cotton candy. Binders are added for strength and stability. The resulting product is cut to size. Remnants are recycled.

Glass wool fiber itself provides very little insulation value. It is the “package” that holds millions of dead air spaces. Trapped air is the actual insulator.

Glass Wool Insulation Uses

After the manufacturing process, glass wool is turned into many different types of insulation products.

Glass Wool Insulation Batts and Blankets

Batts installed in wall stud cavities are the most common and recognizable use of glass wool batts. Rolls or batts are also used in attics, rafters, and floors. They are available faced or unfaced. The kraft paper faced product acts as a vapor barrier. Both are R-3.7 per inch.

Rigid Glass Wool Boards

Rigid glass wool boards have an R-value of R-4.3 per inch. Often used in place of rigid polystyrene boards because of its fireproof qualities. It is used on roofs, ceilings, partition walls, and in high-temperature locations such as mechanical rooms.

Loose-Fill Glass Wool

Loose-fill glass wool closely resembles bits of cotton. It is a popular attic insulation due to its ease of application–either by contractors or as a DIY project. It has an R-value of R-3.1 per inch–a little less than cellulose insulation.

Glass Wool Duct and Pipe Insulation

Glass wool is manufactured in a rigid form to insulate ducts and pipes. It is available in multiple sizes to fit round ducts. Rigid boards can be cut and fit onto rectangular shapes. Some manufacturers are producing complete ducting–round and rectangular–from fiberglass. These products reduce time and costs during installation.


Optimal insulation in a home makes for more comfort, saves on energy costs, and keeps the building quieter. Glass wool satisfies all three requirements.

  • Thermal Resistance. Batts: R-3.7 per inch. Loose-fill: R-3.1 per inch. High-density rigid boards: R-4.3 per inch.
  • Versatility. Manufactured into many types of products for different applications.
  • Non-combustible. Does not fuel fire or spread flames. (It will melt if it gets hot enough.)
  • Soundproofing. Reduces airborne noise.
  • Safe. Safe to manufacture and install. No volatile organic compounds (VOC) or off-gassing.
  • Easy to Install. Lightweight and flexible. Easy to install, store, and transport.
  • Cost. Costs less than most other types of insulations. Unfaced R-13 about $0.90 – $1.65 per square foot supplied and installed. Faced R-13 about $1.10 – $1.90 per square foot supplied and installed. Material only costs are approximately half.


Glass wool insulation does have a few negatives that you should be aware of.

  • R-value. R-values are generally a little lower than competing products such as cellulose and rigid form boards.
  • Moisture. Absorbs and holds moisture–reducing r-value. Difficult to dry out. Wet glass wool batts have an R-value of zero.
  • Health. Older fiberglass could cause serious skin irritation and breathing problems. Improvements in binders and manufacturing have reduced the problems. Gloves, masks, safety glasses, and tight clothing are still recommended.

Is Glass Wool Eco-Friendly?

Some manufacturers are now using up to 80% recycled glass in their products and there is no shortage of sand. New and improved binders reduce the “itch factor” and it was removed from the cancer-causing carcinogen list in 2011.

The production of glass wool uses up to 10 times more energy than some competing products. It is not recyclable and goes to landfills at the end of its useful life or when soaked and useless.