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Insulation - Chapter 17

By HHI Staff

Insulation is used in a variety of locations in houses: inside walls and roof systems, under floors, and around foundations. Water heaters and ductwork are also commonly insulated. Insulation is required in warm climates to keep the heat outside and in cold climates to keep the heat inside. There are a variety of different types and forms of insulation available. Some are suited for use in specific parts of a house. Nearly every type of insulation has been implicated in some health problem yet, with care in installation and material selection, a healthy house can contain insulation. (This article is from the archives of the original Healthy House Institute, and the information was believed accurate at the time of writing. From "The Healthy House: How to Buy One, How to Build One, How to Cure a Sick One" © 2000 by The Healthy House Institute).


All materials resist the flow of heat to some degree. Dense, solid materials such as steel and concrete resist the flow of heat, but they do a poor job of it. Insulating materials tend to resist the flow of heat very well. Most insulating materials do so by trapping tiny multiple pockets of air within their structure.


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Insulations are compared by their R-value (Resistance-value). The higher the R-value, the better the insulating ability. A common brick has an R-value of 0.20 per inch while fiberglass batt insulation has an R-value of 3.17 per inch. Both materials can be used to insulate a house, but fiberglass does a much better job, in fact it’s over 15 times as effective. Insulating houses in a very good idea because, according to the North American Insulation Manufacturer’s Association (NAIMA), spending $1 on insulation will save $12 in energy costs.

Historically, natural materials were used as insulations. Such things as cotton, straw, sawdust, feathers, moss, and cork were common. Today, most commercially available insulations are man-made. Rock wool and fiberglass were two of the first to be developed. These were followed by perlite, cellulose, and various plastic foams. Asbestos was used in the past in some insulations. It was not as widely used in residences as in commercial buildings, nevertheless, asbestos can be found in some houses, especially around older heating systems.

Health Problems

Of all the health problems related to building materials, insulation seems to have gotten the most press coverage. This dates back to the energy crisis of the 1970s when urea-formaldehyde-foam insulation was responsible for elevated formaldehyde levels in some homes. As a result of health complaints, this particular product was banned from being used in houses. While the ban is no longer in effect, urea-formaldehyde-foam insulation has virtually disappeared from the market. But, since that time, the press and the public have been very interested in the negative health effects of all forms of insulation.

There are actually a variety of health problems associated with the many different insulating materials now on the market. Some illnesses have been found in factories where insulation is manufactured, and sensitive individuals report symptoms related to outgassing. Other problems are related to the release of tiny fibers. Some products are more offensive than others, but none seem to be as bad as urea-formaldehyde-foam insulation. Different insulating materials have different health effects, but most of today’s insulations can be used safely in a tightly constructed house where the insulation is well-separated from the living space.


Many synthetic foam insulating materials release extremely toxic gases when heated and burned. This is one of the reasons fire fighters routinely wear oxygen masks when entering a burning building. For the occupants of a burning house, oxygen masks are rarely available. To them, smoke inhalation means toxic gases. In most fires, deaths are due to carbon monoxide and other toxic gases—not flame contact. Building codes require flammable foam insulation to be separated from living spaces by fire-resistant materials such as drywall or plaster.

When installed improperly, insulation can cause some electrical fixtures to overheat and start a fire. This is especially true when recessed ceiling lighting fixtures are covered with attic insulation. Instructions supplied with insulation typically specify the proper clearance that must be maintained between the insulation and lighting fixtures, furnace flues, water heaters, etc. If a device isn’t specifically designed to be in direct contact with insulation, three inches of clearance should be provided to minimize the chance of fire.

Energy conservation—and insulation in particular—has often been blamed for indoor air pollution and, consequently, ill health. Ill health is not so much due to the insulation itself, but to a failure to design and build the house as a system. Excessive tightening is not a problem—in fact, tight construction is very desirable—as long as the interior of a house is built with low-tox materials, and air is exchanged mechanically.


Batt Insulation


Batt or blanket insulation is very widely used today. It is a fluffy product that can be purchased in different colors, depending on the manufacturer, and in different thicknesses and widths. There are three basic types available for residential use: fiberglass, rock wool, and cotton. Other specialized batts are used in industrial applications. While rock wool was very popular before World War II, fiberglass is now more popular in residential construction. Both are considered man-made mineral fibers and are referred to as mineral wool. Cotton-batt insulation is a relatively new product, designed to appeal to environmentally conscious individuals.

Residential batt insulation is usually sold either without any facing, or with an asphalt-coated Kraft-paper facing. In addition, some manufacturers also offer plastic or aluminized-paper facings. These facings are designed to act as diffusion retarders. In some cases, builders will install a separate diffusion retarder over unfaced batt insulation.


Installers of both rock wool and fiberglass often complain of itching and tiny cuts in the skin due to the fibers. Itching can also result from an allergic reaction to the binder used to hold the insulation together.
There has been a great deal written about the health effects of fiberglass. As early as 1955, researchers were seeing respiratory problems and death attributed to inhaling fiberglass. One of the first reports to gain widespread attention was presented to a World Health Organization symposium in 1986. The report found that workers in fiberglass manufacturing companies suffered more lung cancer than other workers. Other reports have also indicated that man-made mineral fibers such as rock wool and fiberglass can cause cancer in production workers. The illnesses reported include cancer of the upper respiratory system, alimentary tract, and digestive system, as well as non-malignant respiratory disease. Production workers are usually exposed to higher concentrations over longer periods of time than homeowners. Insulation installers can be exposed to levels even higher than production workers because they often work without respiratory protection.

Some people believe the increased cancer risk is due to short, small-diameter fibers that are inhaled—fibers that are similar in size to asbestos fibers. One report suggests that these man-made mineral fibers “appear to be more potent than asbestos with regard to chronic pulmonary disease.” The U.S. National Toxicology Program’s Seventh Annual (1992) Report on Carcinogens, said that fiberglass is “reasonably anticipated to be a carcinogen.” Fiberglass insulation now carries a warning label stating that it is a possible carcinogen. Manufacturers recommend the following work practices: wear a respirator; avoid contact with skin and eyes; wear long-sleeved clothing, gloves, and eye protection; wash with soap and water after handling; wash work clothes separately from other clothes and wipe out the washing machine.

Fiberglass manufacturers point out that fiberglass and asbestos are chemically different, and that when asbestos gets into the lungs, it remains unchanged and stays there forever, but that fiberglass eventually dissolves in body fluids. Richard Munson, a vigorous opponent of fiberglass (and a proponent of cellulose insulation) says that when fiberglass dissolves in the lungs, the decomposition produces silicic acid, which is a cytotoxin. Cytotoxins kill living cells.

There are a number of situations where homeowners have had their health destroyed by fiberglass insulation. In one case, fibers were distributed throughout the house during a remodeling project. Everything in the house was contaminated, and the residents complained of an unbelievable list of symptoms: conjunctivitis, dermatitis, intestinal and urological disorders, immunological imbalances, chronic chemical sensitization, heart irregularities with accompanying chest pain, acute nervous teeth causing temporal mandibular joint syndrome, acute sinus headaches, migraine headaches, tracheitis, tonsillitis, sinusitis, tachycardia, acute eczema and psoriasis, acute depression, anxiety, and tension. Another case involved fibers migrating into the living space from blown-in attic insulation.

It’s been found that when moisture is present in mineral-wool insulation, the resin binder can break down and release aliphatic aldehydes, and residents can complain of odors. Moisture in insulation can also lead to biological growth and reduced insulating ability. When done properly, tight construction minimizes these hidden moisture problems.


The negative health effects related to fiberglass insulation have been widely disseminated by a group called Victims of Fiberglass (VOF). While there is some good scientific evidence regarding negative health effects and fiberglass, VOF has often taken an alarmist view, suggesting that fiberglass is worse than asbestos, and should be removed from all houses. Yet, in many houses, the migration of fibers into the living space is negligible. In tightly constructed houses, the insulation, no matter what kind it is, is well-separated from the occupants.




Fiberglass insulation is manufactured by melting inorganic materials—often sand—and spinning them into glass fibers. The fibers are usually held together in batt form by a formaldehyde-based binder. Fiberglass is generally contaminated with fewer impurities than rock wool and its cost is somewhat less.


Most of the fiberglass insulation manufactured today is either pink or yellow in color, and the batts contain approximately 5% of the resin binder. The pink variety contains, in addition, less that 1% dye to give it the pink color. The yellow insulation has been recommended for chemically sensitive individuals, because of an intolerance to the coloring dye. This seems to be a reasonable precaution—avoid as many unnecessary pollutants as possible—however, the formaldehyde binder is more problematic than the dye. With age, outgassing from the binder will diminish, and if the insulation is well separated from the living space (by using tight construction techniques), neither odors nor fibers will reach the occupants.


Owens-Corning Fiberglas Corp. introduced a fiberglass insulation called Miraflex in late 1994 that seems to have some health advantages when compared to conventional fiberglass batts. Miraflex is produced by fusing two different types of glass into long strands that are more resistant to breakage—and no formaldehyde binder is used. In addition, this insulation is wrapped with a layer of perforated polyethylene. The wrapping minimizes fiber release when handling. The wrap is perforated to prevent trapping moisture in the insulation. Miraflex is less of a problem than more conventional products, but it only comes in a few standard sizes, so it cannot be used in all residential applications. However, the manufacturer is adding new sizes to the line occasionally.


Johns-Manville Corp. has a fiberglass insulation called Grid-SHIELD Rx that uses an acrylic resin, rather than a formaldehyde-based resin. It is wrapped with a perforated polyethylene, which can minimize the release of fibers in applications such as above dropped ceilings. However, the fibers themselves are similar to conventional fiberglass products, so they can be broken off and abraded during handling and cutting. Grid-SHIELD Rx is only available in limited sizes, it’s being marked primarily for commercial applications, and it’s more costly than conventional fiberglass. They also have a similar product called ComfortTherm that is marketed for residential applications.


During a fire, the fiberglass itself is fairly inert, giving off little in the way of toxic gases. The resin, however, can decompose in a fire and produce small amounts of ammonia, carbon dioxide, carbon monoxide, carbon particulates, and traces of hydrogen cyanide. The Kraft-paper facing material can produce oxides of sulfur, carbon, and nitrogen. If a plastic facing is used, it too can give off toxic gases in a fire.


It’s very important to keep fiberglass insulation well separated from the living space. One report found that nearly all of 13 workers in an office reported various symptoms related to glass fibers entering the air due to improper construction methods. Symptoms included: itchy rash, burning eyes, sore throats, coughing, and malaise. Eye complaints made it impossible to wear contact lenses. After the insulation was sealed behind plastic foil, the health complaints ceased.


Rock Wool


Rock wool is produced by heating natural basalt rocks or industrial steel-mill slag in a furnace. As the material melts, it is drawn out into fibers and formed into felts, blankets, or batts. Today, rock wool has been generally replaced in residential construction with fiberglass insulation. While rock wool is better at reducing sound transmission and has better fire resistance, it is generally more costly than fiberglass.


Rock wool is often contaminated with lignite, a type of coal, and mineral oil, to control dust. It is typically bound into batt form by the use of a phenolic resin. These materials can be bothersome to sensitive people if exposed directly.




The cotton insulation currently being manufactured by Inno-Therm Products, LLC is actually a blend of cotton and polyester fibers. (This was formerly made by a company called Greenwood Cotton.) The polyester acts as a binder, holding the fibers in batt form. The cotton insulation manufactured by Bonded Logic uses a thermoplastic resin to hold the fibers together. A binder is necessary to give the fibers a springiness. Neither company uses a formaldehyde-based resin. Much of the cotton for insulation comes from recycled jeans, so it has a bluish color. The cost is similar to fiberglass—but only if you live near the manufacturer. If cotton insulation must be shipped across the country, it will be somewhat more expensive than fiberglass. Cotton insulation is available in several standard sized batts, but not as many sizes as fiberglass or rock wool.

Although cotton insulation is billed as a healthy product—and it’s certainly much better than fiberglass or rock wool—it isn’t perfect. In order to get building-code approval, it’s treated with something like boric acid to make it flame resistant. Placing a sample up to your nose an inhaling can result in burning sinuses because of the boric acid.

Workers who inhale cotton dust in cotton-processing industries are at risk of contracting byssinosis, which is also known as brown lung disease. Although there is no evidence that cotton insulation installers would also be at risk, respiratory protection is recommended.

In the U.S., almost half the pesticides used in agriculture are applied to cotton—far more than any other crop. Some of this residue remains in the cotton after processing, so it could result in some minor contamination of cotton insulation. Pesticide residues may explain why some chemically sensitive people must wear clothing made from organically raised cotton.

Even though it is not ideal, cotton insulation is a relatively healthy product. However, to be safe, it should be well-separated from the living space, just like man-made mineral fiber insulation. And, of course, tight building techniques have other advantages, as discussed in Tight Construction.

Loose-fill and Blow-In Insulation

Loose-fill and blow-in insulations come in several forms. Some can be simply poured out of a bag while others are blown through a specially designed machine, then through an applicator hose. Cellulose and chopped fiberglass are the most common. Both are generally blown in place but they can also be poured out and placed by hand.


Sometimes, the only way to insulate the walls of an existing house is to drill holes in the walls and blow some type of insulation into the wall cavities. Existing attics can be insulated in a variety of ways, but blow-in insulations are often quicker are cheaper to install than batts. Some lumber yards rent blowing machines to do-it-yourselfers. When carefully blown into sidewalls, insulation can help to tighten a house, thus minimizing infiltration, and maximizing energy efficiency and comfort.


For new construction, there is a Blow-In-Blanket system (BIBS), licensed by Ark Seal International, that uses either cellulose or chopped fiberglass. With this approach, a mesh is stapled up over the studs, on the interior—after the wiring and plumbing are in place, but before the drywall. Then cellulose insulation (or chopped fiberglass) is blown into the stud cavities. This will fill voids quite well around electrical boxes and plumbing pipes, and it is often faster than using batts.


Cellulose and chopped fiberglass are widely used in wood frame construction. Vermiculite, perlite, and polystyrene beads are more often found in masonry construction. They can simply be poured into the inside of a concrete block wall as it is being built. Materials like shredded tree bark and sawdust have been used in the past as loose-fill insulation, but they are very susceptible to insect attack and fire, so they are almost never used today.




Cellulose insulation is a very popular product today. It is made by chopping old newspapers into a fine, fluffy material. Because newspapers are very combustible, and they can be eaten by insects, fungi, or bacteria, and they can be used as nesting material by rodents, cellulose insulation must be chemically treated. Approximately 20% of the final product consists of additives such as borax, boric acid, ammonium sulfate, aluminum sulfate, lime, ammonium phosphate, mono- and diammonium phosphate, aluminum hydrate, aluminum trihydrate, and zinc chloride. If used in improper amounts, these chemicals may not adequately control flammability, and they can corrode any metal they come in contact with. In attic areas, roof trusses are often held together with metal plates. Corrosion of these plates could eventually lead to a collapse of the roof system. Cellulose insulation standards today take these potential problems into consideration, but many older products could contain flammable or corrosive material. A sample of the insulation can often be obtained from the attic and placed near a flame to test for flammability, and an examination of any exposed metal will reveal any corrosion.


From a health standpoint, the various chemical additives can cause reactions in some sensitive occupants. Symptoms reported after the installation of cellulose insulation include: severe rashes, hair loss, digestive and respiratory disorders. Individuals with an intolerance to newspapers (either to the printing ink or to the paper) can easily be bothered by this insulation. Because cellulose insulation is so finely ground and powdery, it can filter through very small openings into the living space, resulting in symptoms that require costly removal. Installers who don’t wear protective clothing or respiratory protection can experience red and sloughing skin, lung irritation, coughing, bronchitis, and pneumonitis.


A 1993 paper (which was funded by the fiberglass-insulation industry) found few research reports directly related to health effects of cellulose insulation. However, some indirect evidence was reported. For example, excess cancers and pulmonary disease have been seen in paper-mill workers and cellulose insulation is made from paper. Sub-lethal doses of boric acid have caused symptoms of abdominal pain, and liver, kidney and lung dysfunction. An experimental study in which rats inhaled cellulose insulation, resulted in pulmonary damage.


Cellulose insulation is often installed in existing wall cavities through small holes drilled in the exterior siding, which are plugged after the cavity is filled. There are some real horror stories of applicators working their way around the outside of houses without realizing they were blowing large amounts of insulation into the interiors. In older houses, remodeling over the years may have left openings in the walls of closets, above dropped ceilings, or behind kitchen cabinets. As a result, a house can have clouds of insulation floating around inside—unknown to the applicators outdoors. Small gaps around electrical outlets can be easy pathways for insulation to enter the living space of a house. Because of this, it’s always a good idea for someone to be inside the house while the material is being installed. That way, any problem will be noticed immediately—before an extremely difficult clean-up job is necessary.


There are a number of cases where homeowners have experienced a wide variety of negative health effects related to cellulose insulation. This is usually the result of the dry insulation migrating into the living space because of sloppy installation. Symptoms of breathing difficulties, rash, skin turning yellow, hair falling out, bronchitis, sore throat, mood swings, suicidal depression, bleeding gums, and abdominal pain have all been reported. Tropical fish have died, house plants have suffered, and a dog has gone into convulsions—all after cellulose insulation was poorly or improperly installed.


In most cases, cellulose insulation is installed conscientiously and it remains inside building cavities, so it presents no health problems to the occupants. However, small amounts (sometimes large amounts) can be blown into the living space of an existing house during installation, and installers must be careful to minimize such occupant exposure, and then clean up thoroughly. New houses can also be insulated with cellulose, and if they are constructed tightly, the insulation won’t be able to migrate into the living space. There are many manufacturers of cellulose insulation, and it can be purchased through many lumberyards or insulation contractors.


Chopped fiberglass


This material can be installed in a manner similar to cellulose. It is composed of small fibers of glass, similar to fiberglass batt insulation, but in a loose form, so it can be blown into wall cavities or attic spaces. Glass is inherently non-combustible and is not subject to being eaten, so it does not need to be chemically treated like cellulose.


Several manufactures make a chopped fiberglass blowing insulation. Certainteed Corp. has a widely used product, called Insulsafe, that contains approximately 1% mineral oil and silicone to control dust. This is the least chemically contaminated mineral-fiber insulation available today for the residential market. For many sensitive people, this is a positive point, but it must be weighed against the possible long-term cancer risks. If it is adequately separated from the living space using tight construction techniques, the risk will be minimal for the occupants.


Much of the concern over the cancer causing ability of man-made mineral fibers relates to very small diameter fibers. Insulsafe, in particular, is reportedly more problematic than other products because of its small fiber size.


Rock wool


Many older homes are insulated with loose rock wool, primarily in their attics. Installed by simply pouring it in place, its use today in the residential market is considerably less than it was in the past. It can be contaminated with the same materials that rock-wool batts contain, with the exception of the resin binder. Sensitive people should be concerned about its presence, but should keep in mind that old insulation will have outgassed over the years and may no longer be a outgassing problem. However, inhalation of the loose fibers can still be a cancer risk.


Vermiculite and perlite


These materials are usually poured-in-place, sometimes in attics, but more often inside hollow concrete blocks. Vermiculite is a mica-like mineral that contains both free and chemically bound water. When heated, it expands due to steam being driven off. This puffed-up product is then used for insulation. It’s naturally resistant to fire, rot, vermin and termites, but is sometimes treated chemically to make it water repellent.
There is some concern about vermiculite containing small amounts of asbestos, however, the temperatures used in heating and puffing it up may cause the asbestos to decompose, yielding a less-toxic product. Still, it has been reported that one particular vermiculite mine produced vermiculite with up to 5% asbestos. It is estimated that 70% of the vermiculite in use today came from this single mine, with the asbestos-contaminated product being installed in 940,000 homes. Fortunately, this particular mine was shut down in 1990. The EPA suggests that vermiculite should be treated like any other asbestos-containing material.


Perlite is a naturally occurring silicate volcanic rock. When heated, it expands, like vermiculite, because of a small amount of water turning to steam. Perlite is also fireproof and resistant to vermin. It is a very dusty material, and is often treated with silicone to control the dust. Its use in attics is often discouraged because the dust can filter down into the living space through light fixtures or other small openings. This dust can be problematic to an asthmatic, as can the silicone to chemically sensitive individuals. There is the possibility of silicosis due to long term breathing of dust containing silica, but this is a remote possibility outside of a perlite-producing factory.


When these products are used inside masonry walls, there is little chance of them or their contaminants reaching the living space—unless the walls have cracks in them and air-pressure differences cause air to move through those cracks. Unfortunately, older masonry walls are often cracked. In older attics, there are even more possibilities that they can get into the living space, because older attics are often not sealed particularly well. In new construction, extra care should be taken to insure that they stay inside building cavities and remain well-separated from the living space.


Polystyrene beads


Polystyrene beads, which are often used as stuffing in bean-bag chairs, can also be used as a loose-fill insulation. The beads, when expanded, are approximately 1/8" in diameter. As with many synthetic foam insulations, they are flammable and must be protected from fire. Like vermiculite and perlite, they are primarily used to insulate inside masonry walls—although they can also be used in attics and in other locations. Health concerns are similar to polystyrene board products (see below).

Board Insulations

There are a number of different insulating boards. Those commonly used in residential applications include: polystyrene, polyurethane, isocyanurate, cellular glass, rock wool, and glass fiber. Cork, phenolic foam, and rubber foam are occasionally used.


One of the biggest issues with the synthetic foam insulations has to do with the gases used to manufacture them. In the past, some of these products used chemicals called chlorofluorocarbons (CFCs) that were found to damage the ozone layer. Today, manufacturers have switched to less-damaging HCFCs. Although not as bad as CFCs, HCFCs still damage the ozone layer.


Most board insulations are available in a variety of thicknesses and sizes. Four-foot by eight-foot sheets are common. They are often used as sheathing, underneath the siding of a house, or as foundation insulation.




Polystyrene foam insulation is made in two types, expanded and extruded. Expanded polystyrene consists of small beads fused together inside a mold. It is often called beadboard. Extruded polystyrene is made by pushing a chemical mixture through a rectangular die. Upon cooling, it is cut into sheets. Both types of polystyrene will deteriorate when exposed to ultraviolet light, so they must be protected from sunlight. Both can emit noxious gases when burned.


Expanded polystyrene insulation has never used either CFCs or HCFCs. Instead, it uses pentane in the manufacturing process. Pentane doesn’t damage the ozone layer, but it does contribute to smog. Beadboard’s R-value is slightly lower than extruded polystyrene and it is not as sturdy.


Extruded polystyrene is foamed by the use of the pressurized gas, usually a type of fluorocarbon. After foaming, it will contain, within its pores, both air and the fluorocarbon gas. CFCs, which are implicated in damaging the ozone layer in the upper atmosphere, used to be widely used, but most manufacturers are now using a less-damaging HCFC gas.


Both types of polystyrene insulation are commonly available at lumber yards. Styrofoam is a particular brand of extruded polystyrene that is manufactured by Dow Chemical Corp.


Polyurethane and polyisocyanurate


The basic ingredients of polyurethane foam are isocyanates, polyol resins, and an amine catalyst. Other additives can be used. A blowing agent causes the mixture to expand, creating a foam. Polyurethane can be made into flexible foam, as used in upholstery, or a rigid foam, as used in insulation, depending on the type of isocyanate used.


Health effects in factories that produce polyurethane include: blurred vision, skin, eye and respiratory tract irritation, asthma, chest discomfort, etc. Some of the chemicals causing these symptoms outgas rather quickly, but others do not. Isocyanates are sensitizers. This means that they can sensitize a person and, once sensitized, that person will react to lower levels with a symptom such as asthma. Once these foams are cured, they no longer act as sensitizers.


Polyurethane is flammable and must be separated from the living space by drywall or plaster. It burns rapidly and releases carbon monoxide, oxides of nitrogen, and hydrogen cyanide. Hydrogen cyanide is lethal (it’s used in gas chambers) but so much carbon monoxide is released in a fire that it’s of more concern. A group of firemen, who were exposed to isocyanates, reported numerous neurological symptoms such as: euphoria, headache, difficulty concentrating, poor memory, and confusion.


Polyurethane insulation has a higher R-value than some other insulations because of the blowing agent trapped in its pores. Other insulations use trapped air to retard the flow of heat, but the gas used in polyurethane functions as a better insulator. However, as the material ages, the gas slowly escapes and is replaced with air. This results in a lower R-value as the insulation gets older. The escape of gas can be largely prevented by coating the polyurethane with a dense skin, or a layer of metal foil. Polyurethane used, for example, inside a sealed steel entrance door, would probably allow little gas to escape.


Polyurethane will degrade and fall apart in sunlight unless ultraviolet inhibitors are used in the formulation. It will also take on water when in a damp environment or used underground, so it must be adequately protected with a suitable diffusion retarder.


Polyisocyanurate foam insulation is very similar to polyurethane, but is slightly more stable. It, too, must be protected from sunlight and moisture and it has similar characteristics when burned. It is often supplied with a foil facing to protect it from degradation.


While workers in manufacturing plants can be exposed to a variety of chemicals, polyurethane and polyisocyanurate insulations are fairly inert once cured.


Cellular glass


Cellular glass insulation is a commercial product, and is rarely used in residential applications because of its increased cost. It’s mentioned here because it will not burn and it’s moisture resistant. It can be used in roof and wall systems as well as underground. Various thicknesses are available. Foamed glass is basically composed of glass—it has no fillers or binders—however it is not 100% safe. During the foaming process, carbon-monoxide and hydrogen-sulfide gases are trapped in each cell of the foam. Theoretically, they will not be released because each cell is totally surrounded by glass. But whenever the surface is scratched, or the material is flexed sufficiently, the characteristic rotten-egg odor of hydrogen sulfide can by released. Once incorporated into a building, it is doubtful if this will ever become a problem because, when installed, it’s generally not subjected to abrasion, and most buildings do not flex enough to allow the release of gas. Cellular glass costs approximately two to three times more than other foam insulations, and it has a lower R-value. It’s manufactured under the name of Foamglas by Pittsburgh Corning Corp.


Rock-wool and glass-fiber


These insulation board products have the same basic health advantages and disadvantages as their batt counterparts. They are denser and more-rigid, but are made of the same materials as rock wool and fiberglass batts, although they may contain more resin binder.




Cork insulation is made by grinding up the outer bark of an evergreen oak tree that grows around the Mediterranean Sea. It is one of the few all-natural insulations still readily available, but it is often processed into sheets by adding a resin to hold the particles together. Sometimes instead of using a resin, manufacturers steam-bake the cork in molds. In this process, the natural resins in the cork hold the particles together, but the sheets end up with a burnt odor.


Sensitive people can react to cork held together with a resin or to steam-baked cork, but most healthy people aren’t negatively affected by either. It is sometimes possible to special order unprocessed raw cork granules directly from the tree, but the price can be high. The granules can be used as a pour-in-place insulation. Because there are only so many cork trees in the world, there is a limited supply of cork insulation.56 Cork can cost ten times as much as fiberglass. Manufacturers of cork insulation include Technicor International (Rector brand), and WE Cork.

Spray-In Place Insulation

There are several types of spray-in-place insulation available. The foam products tend to be about the consistency of shaving cream when applied. They can be injected through small holes in walls, like blow-in insulations, or they can be sprayed onto open walls or attic surfaces. 


Urea-formaldehyde foam


In the 1970s, urea-formaldehyde-foam insulation (UFFI) was installed in approximately 500,000 homes in the U.S. and there were no reported negative health effects among the majority of the occupants. There were, however, many instances where negative health effects were recorded. So many, in fact, that the CPSC banned its use in residences and schools in 1982. Even though the ban was overturned by a Court of Appeals, the CPSC feels that the decision was based on legal and factual errors, and they continue to warn consumers about its dangers. Even though it is again legal to use UFFI, it’s rarely installed today. In fact, it’s considered such a liability in houses that some real estate agencies require that its presence be disclosed to prospective buyers.


The primary problem with UFFI is that, if mixed incorrectly, it released excessive amounts of formaldehyde gas into the living space. This occurred more often in warm weather or in hot attics. Other gases given off included: benzene, benzaldehyde, acetaldehyde, cresol, methylnaphthalene, acrolein, ammonia, and phenol.


Health effects included: eye, nose and throat irritation, cough, headache, dizziness, bronchopneumonia, pulmonary edema, asthma, dermatitis, rhinitis, conjunctivitis, and allergy. Some people were sensitized to many other chemicals as a result of the formaldehyde exposure, leading to a wide variety of symptoms.


The story of the Leyda family relates how they were driven from their home after it was insulated with UFFI. Early symptoms included chest problems: colds, bronchitis, and coughs, then later included red, watering, and painful eyes. Mrs. Leyda became very weak and dizzy and began having irregular heartbeats. Her doctor suspected multiple sclerosis. By the time the problem was related to formaldehyde outgassing, Mrs. Leyda had become hypersensitive to a wide variety of everyday chemicals. They borrowed $15,000 to have the insulation removed, but because of her newly acquired sensitivities, Mrs. Leyda still could not tolerate her home. The formaldehyde had sensitized her so much that the family was forced to abandon their home. Mrs. Leyda now has MCS and must avoid many things that the rest of the population takes for granted.


Individuals interested in having UFFI removed from their homes are advised that it’s very expensive and time consuming, involving major demolition and remodeling. Two Canadian publications are available describing the necessary procedures. Because it has been so long since UFFI has been in use, it is doubtful if any early applications are still problematic. Most of the formaldehyde has probably long since dissipated.




Polyurethane insulation is sometimes sprayed in place in residences, but it is more often used in commercial applications. Disadvantages are similar to polyurethane board insulation. Most of these spray-in-place urethane foams use a chemical known as MDI (diphenylmethandiisocyanate). MDI should be treated with respect. It can sensitize a person by inhalation or skin contact, so it should be used with adequate ventilation, respiratory protection, and gloves. Once cured, products containing MDI are fairly inert and are often well tolerated by sensitive people.


There’s a modified urethane spray-in-place insulation that uses MDI but it’s a water-blown product (rather than CFC blown). Called Icynene Insealation, it’s produced by Icynene, Inc. and licensed to contractors throughout North America. It is sprayed onto wall surfaces as a two-part liquid before the drywall is installed. They also have a version that can be injected into existing wall cavities. The two components react, forming carbon dioxide, which expands the foam. If mixed and installed correctly, it sticks to everything and expands to fill all gaps and openings. Once the foam cures, the surface is trimmed flush with the wall studs and the drywall is installed over it. Once completely cured, this material is often tolerated by chemically sensitive people, and after 30 days there are no detectable emissions. Icynene costs roughly twice as much as fiberglass batt insulation, but it requires no diffusion retarder, and it results in a fairly tight structure. Installing Icynene correctly requires training, skill, and care. One contractor has described sloppy installations where wall cavities were not filled completely—leaving large uninsulated voids. But with a competent installer, Icynene can be a healthy choice.


Aerosol cans of single-component polyurethane insulation are widely available in hardware stores and lumber yards for general purpose use in houses. These products use MDI and cure by reacting with moisture in the air. They can be used to fill gaps around window or door jambs, and holes drilled for electrical wires or plumbing lines. This material does outgas MDI for a short period, so respiratory protection, ventilation, and skin protection are recommended.


Single-component urethane has been used successfully in healthy-house construction in a number of applications. For example, the gap between a window frame and the rough framing of the house can be filled with single-component polyurethane then, once the insulation is cured, and any excess is trimmed off with a knife, aluminum-foil tape is applied over the foam as a diffusion retarder to prevent any residual minor outgassing into the living space. This approach helps make the house airtight, and protects the occupants from minor outgassing.


Many builders use canisters of a two-component urethane foam to fill gaps and cracks when they seal up a house. These products also use MDI, but they cure differently than single-component urethanes. They cure by means of a chemical reaction, rather than by reacting with the moisture in the air. Thus, they actually cure somewhat faster than single-component products. They are also often well tolerated by sensitive people after curing.


Some of these foams expand considerably when they cure—so much that they can warp a window or door jamb. Because of this, some window and door manufacturers don’t recommend them. There are two solutions. You can partially fill a gap, let the foam cure, then fill the gap a little more, allow that to cure, and so on, until the gap is filled. This must be done with care to avoid excessive expansion. Or you can use a foam that doesn’t expand very much.


Aerosol foam manufacturers that offer minimal-expanding products include Convenience Products (Touch ‘n Foam for consumers, Touch ‘n Seal single- or two-component foams for professionals), Fomo Products (Handi-Foam, in a variety of container sizes—some smaller throw-way sizes, some larger refillable contractor sizes with application guns, both single- and two-component foams.), Flexible Products Co. (Insta-Seal, a single-component foam in containers ranging from 12 oz. aerosol cans up to 12 lb. contractor-sized containers with application guns), and Macklanburg-Duncan (Polycel, in both consumer and contractor sizes). These manufacturers also offer expanding foams. Most of these products are generally well-tolerated by sensitive people once cured. Foam sealants and guns can be mail-ordered from Shelter Supply.




Air-Krete has been widely reported to be a non-toxic insulating material. It is a foamed-in-place product and it must be installed by trained technicians72 because, if mixed imperfectly, it can shrink, reducing its insulating effectiveness. If installers are not careful, there can be uninsulated voids inside the walls.


The main ingredients in Air-Krete are magnesium oxychloride (a cementitious material), and sodium silicate (water glass). Both are fairly inert. Fluorescent dye is used to give it a pink color. Compressed air is used on the job to cause the liquid material to become a foam. Air-Krete contains no formaldehyde or asbestos and it has more insulating ability than fiberglass or cellulose.


In new construction, Air-Krete is installed in walls before the interior drywall or plaster is attached. In existing buildings, it is foamed into the wall cavities through holes drilled in either the exterior siding or the interior wall surface. The holes are then plugged or repaired. Attics and masonry walls can also be insulated. After installation, Air-Krete becomes semi-rigid within seconds. Final drying takes two to four weeks.
While Air-Krete seems to be one of the least toxic insulating materials on the market today, there are some sensitive people who report a minor odor—even after several weeks. One extremely sensitive person had to resort to having the Air-Krete removed when she couldn’t tolerate it. Most chemically sensitive people, however, tolerate Air-Krete quite well and report little or no odor after curing. Air-Krete was developed by Air-Krete Inc. and there are several licensed installers around the country.


Fiberglass and cellulose


In new construction, chopped fiberglass or cellulose insulation can be mixed with a tiny amount of water or glue and sprayed into open wall cavities. Then, after a brief drying period—usually a few days—the walls are enclosed in a normal fashion. Fiberglass and cellulose dust can be a significant problem when these products are applied as blow-in insulations. But, because the insulation is slightly damp when sprayed in place, dust is not a problem. Thus, this is a healthier method of applying these materials.


One of the concerns with this wet-spray process of installing insulation is that the added moisture can sometimes result in mold growth. In some worst-case installations, there have certainly been serious problems, but in research carried out in Canada, there haven’t been any moisture problems as long as installers use the proper amount of water.77 Drying of the insulation begins immediately, but complete drying typically takes several months.

Reflective-foil Insulation

Radiant energy can be reflected back where it came from by means of a shiny foil. The foil doesn’t need to be exposed directly to the radiant source—it can be placed inside a wall cavity and still function. For example, radiant heat can pass through drywall, strike the foil and be reflected back where it came from. The only requirement is that there be an air space in front of the foil. A layer of reflective aluminum foil inside a wall with a 3/4" air space in the summer can have an R-value of 3.28 compared to 0.91 for a 3/4" air space without aluminum foil. Some of the claims for much higher insulating values are based on theory, and can be difficult to achieve with conventional construction tolerances and practices.


Reflective-foil insulation is also called builders foil. As an insulation, it is only of minimal value in cold climates80 but it can be cost-effective in hot climates to keep the radiant solar energy out of attics and air-conditioned spaces.


Reflective foils are made of a variety of shiny metals including: aluminum foil, stainless steel, and foil-coated paper. They only reflect radiant energy when they are shiny; so they will not function when covered with dust. The dust factor can be difficult to determine when the foil is hidden inside the structure of the house. Dust is more of a problem in floor systems than in walls or ceiling systems, but it can coat a reflective foil in any location.


Reflective foil can function as a diffusion retarder, even when dusty. In such an application, it’s generally called builders foil. Some reflective-foil-faced cardboard sheathing materials can function both as a sheathing material, a diffusion retarder, and as reflective insulation.


Reflective-foil products are sometimes lightly perforated to allow moisture to pass through. The perforated products will function as reflective insulation, but not as a diffusion retarder. Moisture migration is an important issue with reflective-foil insulations because, if you chose the wrong product for a particular application, you can end up with a moisture-condensation problem hidden inside a wall cavity.
These materials rarely pose any health problems, but some reflective foils are made of aluminized Mylar or aluminized polyethylene which could outgas slightly. On rare occasions a sensitive person will be bothered by printing ink from advertising that is printed on a reflective foil product, but in most installations, they are isolated from the living space.


Reflective insulations come in a variety of forms. The lightest-weight products consist of Kraft paper with aluminum foil on one or both sides. One manufacturer of a light-weight foil/Kraft-paper product is Denny Sales Corp. (Denny Foil). These types of materials are often not very sturdy, and they can get torn in some applications. Innovative Energy, Inc. has a very durable Heatshield product that is reinforced with plastic fibers, as does TVM Building Products. In addition, Advanced Foil Systems offers a durable Aluma-Foil product that is a light-weight foil-faced paper, and an Aluma-Foil Plus that is thinner but has a nylon reinforcing. Parsec has an aluminized mylar product.


Innovative Energy, Inc. (Astro-Foil), Reflectix, and TVM Building Products (rFoil) have foil-faced insulations that resemble bubble-pack packaging material. These products can be used in a variety of insulating applications, including around water heaters, pipes, and ducts.


Because there are no 100%-safe insulations available, care should be taken to insure that they are well separated from the living space. Diffusion retarders help in this regard as far as outgassing is concerned, but tight-construction techniques are the most effective means of separation—to prevent both gases and particles from entering the living space.


Of the readily available products, the foam insulations on the market today are often tolerated by sensitive people, especially Icynene and Air-Krete—but they can be expensive, and they must be installed conscientiously. For someone with severe sensitivities, most insulations can be bothersome when in direct contact—but tolerable when well-separated from the living space. This has been demonstrated in a number of healthy houses in which fiberglass was effectively isolated from the occupants.

(This article is from the archives of the original Healthy House Institute, and the information was believed accurate at the time of writing. From “The Healthy House: How to Buy One, How to Build One, How to Cure a Sick One” © by The Healthy House Institute).







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Insulation - Chapter 17 :  Created on March 9th, 2012.  Last Modified on March 15th, 2012


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