ToxFAQs™ for Synthetic Vitreous Fibers

Spanish: Fibras Vítreas Sintéticas

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This fact sheet answers the most frequently asked health questions about synthetic vitreous fibers. For more information, you may call the ATSDR Information Center at 1-800-232-4636. This fact sheet is one in a series of summaries about hazardous substances and their health effects. This information is important because this substance may harm you. The effects of exposure to any hazardous substance depend on the dose, the duration, how you are exposed, personal traits and habits, and whether other chemicals are present.


Synthetic vitreous fibers are manmade fibrous materials used for thermal and sound insulating purposes. Short-term exposure can cause reversible skin, eye, and lung irritation. Workers from factories making synthetic vitreous fibers used in home insulation showed no increased rates of lung problems. Some refractory ceramic fiber workers showed changes in their chest x-rays, but these changes are not associated with breathing problems. There is no clear association between exposure to synthetic vitreous fibers and cancer in humans. Synthetic vitreous fibers have not been detected in any of the 1,647 National Priorities List sites identified by the Environmental Protection Agency (EPA).

What are synthetic vitreous fibers?

Synthetic vitreous fibers are a group of fibrous, inorganic materials that contain aluminum or calcium silicates, and are made from rock or stone, clay, slag, or glass. They do not occur naturally in the environment, but are widely used for thermal and sound insulating purposes and to reinforce other building materials. There are three categories of synthetic vitreous fibers: 1) glass fibers (fiberglass), including glass wool and continuous filament glass, 2) mineral wool, which contains stone wool and slag wool, and 3) refractory ceramic fibers.

Insulation that is used in homes and buildings is composed of synthetic vitreous fibers. Refractory ceramic fibers are not widely used for building insulation. They are used to insulate furnaces, in replacement of asbestos.

What happens to synthetic vitreous fibers when they enter the environment?

  • Synthetic vitreous fibers can enter the air, water, and soil from the manufacture, use, and disposal of fiber-containing materials.
  • Synthetic vitreous fibers are generally not broken down in the environment.
  • Synthetic vitreous fibers do not dissolve in water or move through soil.

How might I be exposed to synthetic vitreous fibers?

  • When insulation materials containing synthetic vitreous fibers are disturbed, fibers can be suspended in the air and inhaled. Installing your own fiberglass insulation in your home may expose you and your family to synthetic vitreous fibers.
  • Workers who install or remove insulation or who are involved in building maintenance or repair are expected to have the highest levels of exposure to synthetic vitreous fibers.

How can synthetic vitreous fibers affect my health?

When synthetic vitreous fibers are suspended in air they can cause irritation of the eyes, the nose and throat, and parts of the lung. When these fibers contact the skin, they may also cause irritation. These effects are reversible and disappear shortly after exposure stops.

Animal studies show that repeatedly breathing air containing a lot of synthetic vitreous fibers can lead to inflammation and fibrosis of the lung. If pulmonary inflammation continues over a long period of time, a slow build up of scar tissue may occur in the lungs and in the membrane encasing the lungs called the pleura. This effect is called pulmonary fibrosis or pleural fibrosis. Glass fibers commonly used in home insulation materials did not cause fibrosis in animals, but refractory ceramic fibers did.

You are unlikely to develop long-term pulmonary inflammation or pulmonary fibrosis from synthetic vitreous fibers, unless you are exposed to very dusty conditions daily for many years. Studies of workers from factories that make synthetic vitreous fibers used in home insulation materials did not find abnormal numbers of cases of long-term pulmonary inflammation, breathing problems, or changes in chest x-rays. Some workers who made refractory ceramic fibers showed changes in chest x-rays that are called pleural plaques, but their ability to breathe was normal. Pleural plaques are small areas of very mildly scarred pleural tissue.

How likely are synthetic vitreous fibers to cause cancer?

You are unlikely to develop cancer from breathing in air with small amounts of synthetic vitreous fibers. Studies of workers from factories that make synthetic vitreous fibers have not found increased rates of lung cancer or cancer of the pleura, called mesothelioma. Animals exposed for life to air containing refractory ceramic fibers showed increased rates of lung cancer and mesothelioma, but animals exposed to insulation glass wools and stone wools did not.

The International Agency for Research on Cancer (IARC) determined that insulation glass wool, stone wool, and slag wool, and continuous filament glass are not classifiable as to carcinogenicity to humans because of the inadequate evidence of carcinogenicity in humans and the relatively low biopersistence of these materials. IARC determined that refractory ceramic fibers are possibly carcinogenic to humans because of their relatively high biopersistence and the findings of cancer in animals that repeatedly breathed in high levels of refractory ceramic fibers. The EPA has classified refractory ceramic fibers as a probable human carcinogen.

How can synthetic vitreous fibers affect children?

There are no unique exposure pathways to synthetic vitreous fibers for children. It is likely that children exposed to these types of fibers will experience the same effects as adults, such as eye, skin, and upper respiratory tract irritation.

There are no studies that examined whether exposure to synthetic vitreous fibers affect the developments of the fetus, infants, or young children.

How can families reduce the risk of exposure to synthetic vitreous fibers?

Insulating material in attics or walls is the most common source of synthetic vitreous fibers in a home. Avoid disturbing or contacting these materials.

If you install your own insulation, wear protective clothing, respiratory protection, and eye protection, and follow recommendations provided by the manufacturer for installing this material.

If you are exposed to these fibers at work, you may carry fibers home on your skin, clothes, or tools. You can avoid this by showering, and changing clothing before leaving work. Your work clothes should be kept separate from other clothes and laundered separately.

Is there a medical test to show whether I've been exposed to synthetic vitreous fibers?

There are currently no tests specific for synthetic vitreous fibers. A chest x-ray is a common method to determine if you have certain conditions, such as pleural plaques, lung or pleural fibrosis, or mesotheliomas.

Has the federal government made recommendations to protect human health?

The Occupational Safety and Health Administration (OSHA) has set a limit of 5 milligrams of synthetic vitreous fibers as inert or nuisance dust per cubic meter (5 mg/m3) of air for the respirable fraction and 15 mg/m3 for total dust. The voluntary limit for fiberglass and mineral wool is 1 fiber per cubic centimeter.


Agency for Toxic Substances and Disease Registry (ATSDR). 2004. Toxicological Profile for Synthetic Vitreous Fibers. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service.

Where can I get more information?

If you have questions or concerns, please contact your community or state health or environmental quality department or:

For more information, contact:
Agency for Toxic Substances and Disease Registry
Office of Innovation and Analytics, Toxicology Section
4770 Buford Highway
Chamblee, GA 30341-3717
Phone: 1-800-CDC-INFO 888-232-6348 (TTY)
Email: Contact CDC-INFO

ATSDR can also tell you the location of occupational and environmental health clinics. These clinics specialize in recognizing, evaluating, and treating illnesses resulting from exposure to hazardous substances.

Page last reviewed: March 26, 2014