Insulation Hazard Spectrum

Individual products can vary significantly in their chemical content, however there are some types of insulation that generally contain less hazardous materials than others. HBN has researched a variety of insulation products used in the walls, ceilings, and floors of a structure. The products are ranked on a simplified spectrum below.[1] Products in the green categories are typically better options than those in the orange or red, and products in the yellow categories are generally less preferable than those at the top, but are better choices than those at the bottom.

Insulation is a very broad product category that employs a variety of material types, such as cellulose, glass and mineral fiber, plastic foam, and natural materials that are used in a range of forms — batt, blown, sprayed, and board. It is an important component of almost all new construction and many energy-efficiency improvements, and given the quantity of insulation used, it is easy to see how material decisions can cumulatively affect the amount of toxic material brought into building spaces.[2]
                    
Insulation materials can contain a range of hazardous chemicals. Those of highest concern include halogenated flame retardants, formaldehyde-based binders, organotin catalysts, isocyanates, and blowing agents with high global warming potential.                

In general, encourage manufacturers to fully disclose the content and associated health hazards of insulation products through the industry’s collaborative, user-designed open standard, Health Product Declarations (HPD).

Here are some general rules of thumb to use when choosing insulation materials:
  • The top-ranked insulation is expanded cork board, because it is free of hazardous content. However, it is expensive and may not be widely available, requiring advanced planning to allow for its use.
  • Prefer fiber glass and cellulose insulation. Not all products toward the top of the ranking are expensive or limited in availability. Commonly used fiber glass and cellulose insulations are some of the highest ranked from a health perspective, and have the lowest installed cost per given R-value. While the R-value per inch is higher for many foam products, the R-value per dollar is not. For applications with few space restrictions, the same insulative performance can be achieved with these healthier materials.
  • Avoid products with formaldehyde-based binders. Formaldehyde is a carcinogen and respiratory hazard, even at low levels. If products that contain a formaldehyde-based binder must be used, make sure that they meet the California Department of Public Health (CDPH) Standard Method for the Testing and Evaluation of VOC Emissions for residential scenarios.[3]
  • If board insulation is required, prefer rigid mineral wool insulation that meets the CDPH Standard Method for the Testing and Evaluation of VOC Emissions or cork.
  • Avoid foam insulation, whether board or spray-applied, whenever possible. Foam insulations commonly contain highly toxic flame retardants, and spray foam contains asthma-causing isocyanates. If foam insulation must be used, avoid products that are reacted on site, such as spray foam. Also, look for products that do not use halogenated flame retardants. In order to achieve insulation and air sealing, while avoiding spray polyurethane foam, use a combination of lower hazard sealants (such as acrylic caulk or foam sealant tape) and insulation (such as fiber glass or cellulose). 
  • Use mechanical installation methods, such as fasteners, whenever possible to avoid unnecessary use of adhesives.   
             

These recommendations and the following research is based in large part on work done by HBN for a collaborative project with Energy Efficiency for All (EEFA). For additional references as well as more information on the common content of these insulation materials, their typical performance characteristics like R-value, and relative cost, see Making Affordable Multifamily Housing More Energy Efficient: A Guide to Healthier Upgrade Materials
Expanded cork is the preferred choice in insulation in terms of chemical content and hazards. Cork has a long history of serving as an insulator. Well before plastic insulations like polystyrene came to market, cork was used as an insulating material.[4] Present-day cork insulation is produced using granulated bark from the cork oak tree which is compressed with steam until the granules swell and hold together to form slabs. Cork does not require flame retardants or other additives. It is expensive and may not be widely available, requiring advanced planning to allow for its use.

Blown-in fiber glass insulation may be installed as loose-fill (usually used in attic applications where space is not limited), dense-pack (more densely packed for wall cavities to prevent settling), and spray-applied (usually with a small quantity of adhesive to adhere the insulation to the cavity). Dense-pack fiber glass has the advantage that it can be used to upgrade the insulation of enclosed wall cavities.

Blown-in fiber glass insulation is made from individual strands of glass fibers.[5] These products commonly contain a small quantity of carcinogenic dedusting oils, used to keep dust levels down during manufacture and installation. Ask manufacturers to provide options that use safer alternatives, like vegetable oil.

Fiber glass insulation often includes a high amount of recycled content (known as glass cullet), which comes mainly from recycled bottles. However, some glass cullet may be contaminated with recycled cathode ray tubes (CRTs), which release lead into the environment during recycling. Look for fiber glass insulation products containing 60% or more post-consumer recycled content, as these products come from facilities that do not process CRTs.[6]

Batt insulation is made by combining fiber glass strands, a dedusting oil like that used in loose fill insulation, and adding a binder to form batts. As of 2015 all four major manufacturers of residential fiber glass batt insulation now use a formaldehyde-free binder. 

Fiber glass batts come with several facing options: unfaced, kraft paper, foil, or a polyethylene film. Paper is the most affordable and most popular facing option (see below for information on other facing options) and has an asphalt-impregnated paper facer that acts as a vapor retarder. The asphalt material is a substantial part of this type of insulation (typically about 8% by weight), and it contains small quantities of PBT impurities. 

Prefer unfaced batts that use an alternative dedusting oil, such as vegetable oil. Look for fiber glass insulation products containing 60% or more post-consumer recycled content for the reasons cited above for blown-in fiber glass.

Mineral wool is made from a molten mixture of rock and blast furnace slag from the steel industry. The batt insulation is commonly still made using formaldehyde-based binders. Some products that use alternative, formaldehyde-free binders are now available.[7] 

Prefer formaldehyde-free products when using mineral wool insulation. See Mineral Wool Batts and Boards below for more information.
Polyisocyanurate board consists of a foam core made by reacting isocyanates and polyols. This core is sandwiched between aluminum and kraft paper facers or fiber glass mat. 

If using polyisocyanurate insulation, prefer halogen-free products. Most polyisocyanurate boards contain TCPP, a chlorinated flame retardant (part of the larger chemical group of halogenated flame retardants). Halogenated flame retardants are considered a very high concern to avoid because they can be persistent and toxic. Halogen-free polyiso products are a better option, instead using a reactive flame retardant that becomes part of the polymer itself and is assessed to be of relatively lower hazard.[8]

It is not clear what, if any, isocyanates may be released from polyiso products during use, but they clearly present concerns at other stages of their life cycle. Isocyanates used in the production of polyisocyanurate are a leading cause of work-related asthma and also use polluting chemistry in their manufacture.[9] 
Batt insulation made from cotton, cellulose, or a blend of the two contains about 7% boric acid as a flame retardant. Boric acid carries developmental and reproductive hazards which may be a concern, particularly during installation and if dust enters the living space. Government agencies have raised fewer human health concerns about boric acid than for other flame retardants - particularly halogenated flame retardants, which can be persistent and bioaccumulative.

Prefer products that use ammonium phosphate salt rather than boric acid as a flame retardant. Avoid any product for which a manufacturer does not identify the flame retardant.

Blown-in cellulose insulation typically contains more than twice as much boric acid flame retardant as cellulose batts - about 15% of the product by weight. As noted above, boric acid is a developmental and reproductive toxicant, and can be a concern should dust make its way into living spaces. However, as compared to other flame retardants common in insulation, boric acid is less of a concern. Loose fill cellulose also contains a dedusting oil. Though not common, some of these dedusting oils are carcinogenic.

HBN has not identified any blown-in cellulose insulation products on the market that do not contain boric acid. Regardless, preferring products made without carcinogenic dedusting oils is recommended.

Unlike kraft-faced fiber glass batt insulation, batts faced with PSK (polypropylene-scrim-kraft) and FSK (foil-scrim-kraft) tend to be very poorly disclosed by manufacturers. Like kraft-faced fiber glass batts, these products commonly rely on a carcinogenic dedusting oil and asphalt-based adhesive and additionally may include a hazardous flame retardant. For products like duct wrap insulation, some manufacturers may still use formaldehyde-based binders which can emit formaldehyde (a carcinogen and asthmagen) over time.

To minimize hazards, prefer PSK or FSK-faced fiber glass batts that use adhesives that are not based on asphalt. Confirm with manufacturers that products are free of formaldehyde, and ask for products that don't contain halogenated flame retardants.

Mineral wool is made from a molten mixture of rock and blast furnace slag from the steel industry. The fibers are commonly sprayed with a urea phenol-formaldehyde binder and formed into mats or boards, before being put through an oven to cure. Most typically, these batts are unfaced. 

Urea phenol-formaldehyde, like other formaldehyde-based resins, can release formaldehyde (a carcinogen and asthmagen) into living spaces over time. Starting in mid-2017, some mineral fiber batt insulation has become available without formaldehyde-based resins (see above). 

Prefer formaldehyde-free products when possible or substitute other insulation materials higher in this chart. If you must use mineral fiber insulation with a formaldehyde-based binder, prefer those that meet the California Department of Public Health (CDPH) Standard Method for the Testing and Evaluation of VOC Emissions requirements for the residential scenario.[3]

Fiber glass board insulation is made from a core of glass fibers and typically a formaldehyde-based binder. The core is then covered by densely-packed strands of glass fiber and an acrylic coating that protects the boards from moisture and surface damage. The acrylic coating commonly contains a flame retardant and an antimicrobial additive to prevent mold from growing on the coating after installation. Antimony trioxide, commonly used as a flame retardant in these insulations, is a carcinogen that is also a developmental and reproductive toxicant.

Fiber glass board insulation made with a formaldehyde-free binder is beginning to enter the market. Look for these products whenever possible, and use insulation types higher in this chart in place of fiber glass board insulation when applicable.

Expanded polystyrene insulation is made by expanding individual pre-formed beads of polystyrene into a molded shape. Polystyrene coffee cups are made this way. EPS insulation has historically contained the flame retardant hexabromocyclododecane (HBCD) which is highly toxic, persistent in the environment, and bioaccumulative. According to the industry association, their members which account for estimated 80-85% of the EPS insulation manufactured in the United States, have stopped using HBCD. It is not clear whether any of the remaining portion of EPS still contains HBCD. The common replacement flame retardant is still halogenated like HBCD and presents life cycle concerns, including the potential for hazardous break down products.[10] 

Some specialty EPS insulation also contains an insecticide to make it resistant to termites which might otherwise burrow into it when used below grade. A commonly used insecticide is known to be hazardous to bees and is a potential endocrine disruptor.[11]

If using EPS insulation, make sure it does not contain HBCD and ask the manufacturer to disclose the identity and hazards of the alternative used.

Polyisocyanurate board consists of a foam core made by reacting isocyanates and polyols. This core is sandwiched between aluminum and kraft paper facers or fiber glass mat. Polyisocyanurate boards typically contain TCPP, a halogenated flame retardant. Halogenated flame retardants are considered a very high concern to avoid because they can be persistent and toxic.

Some polyiso products that are free of halogenated flame retardants are currently available (see above). Prefer those products over other types of foam insulation, which all contain some form of halogenated flame retardant. 

Expanded polystyrene insulation is made by expanding individual pre-formed beads of polystyrene into a molded shape. EPS insulation has traditionally contained the flame retardant hexabromocyclododecane (HBCD) which is highly toxic, persistent in the environment, and bioaccumulative. Much EPS insulation has transitioned away from HBCD, but some insulation may still contain it.  

Some specialty EPS insulation also contains an insecticide to make it resistant to termites which might otherwise burrow into it when used below grade. A commonly used insecticide is known to be hazardous to bees and is a potential endocrine disruptor.[11]

Extruded polystyrene is made from similar polystyrene beads as EPS, but the beads are extruded into a solid block. The result is that there are fewer pores between the beads which makes XPS an air barrier. XPS has historically contained the flame retardant hexabromocyclododecane (HBCD) which is highly toxic. The major manufacturers of XPS indicate they have transitioned away from the use of HBCD. The common replacement flame retardant is still halogenated like HBCD. The health hazards of this alternative have not been fully studied and it presents life cycle concerns, including the potential for hazardous break down products.[10] 

XPS also relies on a blowing agent that contributes to global warming. As much as 10% of the weight of the board is due to this blowing agent, which is 1,430 times more potent than carbon dioxide at warming the planet.[12] 

Products from smaller manufacturers could potentially still use HBCD. If using XPS insulation, make sure it does not contain HBCD and ask the manufacturer to disclose the identity and hazards of the alternative used.
 
Extruded polystyrene is made from similar polystyrene beads as EPS, but the beads are extruded into a solid block. The result is that there are fewer pores between the beads which makes XPS an air barrier. XPS has traditionally contained the flame retardant hexabromocyclododecane (HBCD) which is highly toxic. XPS with HBCD is no longer common, but these products may still be available. XPS also relies on a blowing agent that contributes to global warming. This blowing agent is 1,430 times more potent than carbon dioxide at warming the planet.[12] 

Spray polyurethane foam insulation is sold as a two-part liquid that is then combined and applied on-site. Part A is a mixture of isocyanates, and Part B is a mixture of polyols and other additives. This reaction produces polyurethane, and releases small amounts of isocyanate and other chemicals into the surrounding area, which can expose installers (and others who may be present) to these hazardous ingredients. Excessive heat release can also lead to fires in extreme cases.

Additionally, while it is generally thought that after 24 hours, the chemical reaction in the foam is complete, evidence suggests that chemical emissions continue for much longer, potentially exposing residents to hazardous chemicals.[13]

Isocyanates are asthmagens and are a leading cause of work-related asthma.[14] The additives typically included in Part B of the foam mixture include an organotin catalyst with reproductive toxicity concerns and a halogenated flame retardant. Halogenated flame retardants are considered a very high concern to avoid because they can be persistent and toxic. Closed cell spray foam also uses a blowing agent that is a highly potent contributor of global warming.

See Careful Insulation Selection and Installation Can Protect R-Value and Health.     

Endnotes
[1] Unless otherwise noted, product content and health hazard information is based on research done by Healthy Building Network for Common Product profiles, reports, and blogs. Links to the appropriate resources are provided.

[2] “Making Affordable Multifamily Housing More Energy Efficient: A Guide to Healthier Upgrade Materials.” Energy Efficiency for All, September 2018. https://healthybuilding.net/reports/19-making-affordable-multifamily-housing-more-energy-efficient-a-guide-to-healthier-upgrade-materials.

[3] The CDPH method is a standard for testing the level of certain VOC emissions (including formaldehyde) from products in a small scale test and then using modeling to represent different real world scenarios. The most protective is the residential scenario, and this should be preferred if available. Most certifications now available are for the private office scenario. Programs that certify the CDPH Standard Method for Testing and Evaluation of VOC Emissions include: GreenGuard Gold, SCS Indoor Advantage Gold, and Berkley Analytical ClearChem.

[4] Bozsaky, Dávid. “The Historical Development of Thermal Materials.” Periodica Polytechnica Architecture 41, no. 2 (n.d.): 49–56. https://doi.org/10.3311/pp.ar.2010-2.02.

[5] It is important to note that while some specialty glass fibers are carcinogens, the glass fibers used in fiber glass insulation are not because they are biosoluble (readily dissolved and cleared from the lungs). In 1988, the International Agency for Research on Cancer (IARC) released a monograph on man-made mineral fibers. This study concluded that mineral wool fibers (including glass and rock or slag wool) were “possibly carcinogenic to humans.” In 2002, new data from additional studies were reviewed and incorporated into a new monograph that concluded that the type of mineral wool fibers used in insulation are, “not classifiable as to their carcinogenicity to humans.” In 2011, both the National Toxicology Program (NTP) and the California Office of Environmental Health Hazard Assessment (OEHHA) made a distinction in their listings between biosoluble glass fibers, which are cleared from the body, and certain other glass fibers that are inhalable and persist in the body (are biopersistent). This change meant that the cancer hazard association and a cancer warning, which was previously required on packaging, were no longer warranted for products using biosoluble fibers. The prior labeling of fiber glass insulation products with cancer warnings has led to some confusion in the industry, but the scientific consensus is that the biosoluble glass fibers that are used in insulation are not carcinogens. Glass fibers from insulation can cause temporary eye, skin, and lung irritation. As with all products, proper personal protective equipment (PPE) should be used for installation or removal of products.         
See: “IARC Monographs on the Evaluation of Carcinogenic Risks to Humans: Volume 81 Man-Made Vitreous Fibers.” World Health Organization: International Agency for Research on Cancer, 2002. http://monographs.iarc.fr/ENG/Monographs/vol81/mono81.pdf.; “IARC Monographs on the Evaluation of Carcinogenic Risks to Humans: Volume 43 Man-Made Mineral Fibers and Radon.” World Health Organization: International Agency for Research on Cancer, 1998. http://monographs.iarc.fr/ENG/Monographs/vol43/mono43.pdf.; “Modification of the Listing of Glasswool Fibers (Airborne Particles of Respirable Size) to Glass Wool Fibers (Inhalable and Biopersistent).” OEHHA, November 18, 2011. https://oehha.ca.gov/proposition-65/crnr/modification-listing-glasswool-fibers-airborne-particles-respirable-size-glass.; “New Substances Added to HHS Report on Carcinogens.” NIEHS, June 10, 2011. https://web.archive.org/web/20110817141807/http://www.niehs.nih.gov:80/news/releases/2011/roc/.; “ToxFAQsTM for Synthetic Vitreous Fibers.” Toxic Substances Portal - Agency for Toxic Substances & Disease Registry. Accessed June 14, 2017. https://www.atsdr.cdc.gov/toxfaqs/tf.asp?id=907&tid=185.    

[6] The high temperature process used to create glass fibers during insulation manufacturing drives off lead compounds and other heavy metals from glass cullet, so they are unlikely to remain in the final product. These releases during processing are, however, a potential concern for workers and surrounding communities. In most cases, reported releases of heavy metals from fiber glass insulation manufacturing facilities do not raise alarms, but in some cases the levels of releases point to potential supply chain quality control issues. These issues are largely localized to a few plants reporting disproportionately high levels of lead releases. For more information on glass cullet recycling see our blog post and the full report linked there.

[7] “Formaldehyde-Free Thermafiber® Mineral Wool Insulation.” Owens Corning. Accessed May 3, 2017. https://www.owenscorning.com/formaldehyde-free.; “AFB Evo Technical Data Sheet.” Rockwool, January 1, 2018. https://cdn01.rockwool.com/siteassets/o2-rockwool/documentation/technical-data-sheets/commercial/AFB-evo-Formaldehyde-Free-Techdata.pdf?f=20181016101455.

[8] “EnergyGuard NH Polyiso Insulation Health Product Declaration.” GAF, March 15, 2018. https://hpdrepository.hpd-collaborative.org/repository/HPDs/publish_112_EnergyGuard_NH_Polyiso_Insulation_1521152481.pdf; “SecurShield NH Polyiso Insulation Product Data Sheet.” Carlisle, April 6, 2018. https://www.carlislesyntec.com/view.aspx?mode=media&contentID=6139.  

[9] US EPA, OCSPP. “Potential Chemical Exposures From Spray Polyurethane Foam.” Overviews and Factsheets. Accessed March 30, 2017. https://www.epa.gov/saferchoice/potential-chemical-exposures-spray-polyurethane-foam; Vallette, Jim. “Chlorine and Building Materials: A Global Inventory of Production Technologies, Markets, and Pollution - Phase 1: Africa, The Americas, and Europe.” Healthy Building Network, July 2018. https://healthybuilding.net/reports/18-chlorine-building-materials-project.

[10] Vallette, James. “HBCD-Free StyrofoamTM Insulation Coming to USA.” Healthy Building Network Blog, July 8, 2016. https://healthybuilding.net/blog/463-hbcd-free-styrofoam-insulation-coming-to-usa.; Bienkowski, Brian. “‘Environmentally Friendly’ Flame Retardants Break down into Potentially Toxic Chemicals.” Environmental Health News, January 9, 2019. https://www.ehn.org/environmentally-friendly-flame-retardants-break-down-into-potentially-toxic-chemicals-2625440344.html.

[11] Vallette, James. “Bees Need Healthy Buildings Too.” Healthy Building Network Blog, March 26, 2015. https://healthybuilding.net/blog/431-bees-need-healthy-buildings-too.

[12] US EPA, “Global Warming Potentials and Ozone Depletion Potentials of Some Ozone-Depleting Substances and Alternatives Listed by the SNAP Program,” last updated November 6, 2014, http://www3.epa.gov/ozone/snap/subsgwps.html

[13] A microchamber emission study published by the National Institute of Standards and Technology (NIST) concluded that, “emissions from SPF can be highly variable.” TCPP, the common chlorinated flame retardant used, was detected in emissions from all four samples tested, including one that was tested 18 months after application. Other chemicals were found to be emitted as well. One sample, taken from a residential application of closed-cell SPF (applied during the summer of 2015 and tested March 2016), emitted more than 80 different chemicals. As the study’s authors note, these chemicals may not all have negative health impacts, but some most likely do, including the carcinogens 1,4-dioxane and 1,2-dichloropropane. See: Poppendieck, Dustin G., Mengyan Gong, and Lauren E. Lawson. “Lessons Learned from Spray Polyurethane Foam Emission Testing Using Micro-Chambers.” In The 59th Annual Polyurethanes Technical Conference. Baltimore, MD, 2016. http://ws680.nist.gov/publication/get_pdf.cfm?pub_id=921259.
See also: US Environmental Protection Agency. “Vacate and Safe Re-Entry Time for Spray Polyurethane Foam Application.” Overviews and Factsheets. Accessed March 7, 2017. https://www.epa.gov/saferchoice/vacate-and-safe-re-entry-time-spray-polyurethane-foam-application

[14] US EPA, OCSPP. “Potential Chemical Exposures From Spray Polyurethane Foam.” Overviews and Factsheets. Accessed March 30, 2017. https://www.epa.gov/saferchoice/potential-chemical-exposures-spray-polyurethane-foam.

Last updated: April 2, 2019