Insulation Hazard Spectrum

The Healthy Building Network has researched a variety of insulation products used in the interior walls, ceilings, and floors of a structure. We rank these products on a simplified spectrum below. Products appearing green are better options than those that appear red, and products that appear yellow are generally less preferable to those at the top, but better choices than those at the bottom.

Some general rules of thumb to use when choosing an insulation include:

  1. Avoid products with formaldehyde-based binders. Formaldehyde is a potent carcinogen and respiratory hazard, even at low levels. Fiberglass and mineral wool insulations have traditionally used these binders, but there now are often formaldehyde-free options. See the chart below for details.

  2. Fiberglass insulation often includes a high amount of recycled content (known as glass cullet), which comes mainly from recycled bottles. However, some glass cullet comes from recycled cathode ray tubes (CRTs), which release large amounts of lead into the environment during recycling. Look for fiberglass insulation products containing 60% or more post-consumer recycled content, as these products come from facilities that do not process CRTs.

  3. Avoid foam insulation. Foamed products like polystyrene (commonly called Styrofoam(™)) and spray polyurethane foam use blowing agents that are potent greenhouse gases. These gases contribute to global warming, and detract from these insulations’ positive effects on climate change by saving energy. Foam insulation also contains highly toxic flame retardants.

  4. In situations where you are looking for both air sealing and insulation properties, consider using a caulk and/or tape to seal gaps before installing insulation to achieve both these goals without using spray foam.

While not inexpensive, cork insulation is far and away the best choice in insulation when considering healthy materials. Before plastic insulations like polystyrene came to market, cork was a common insulating material in Europe. Bark from the cork oak tree is granulated, and compressed with steam until the granules swell and hold together to form slabs. Cork does not require flame retardants or other additives.

Loose fiber glass insulation is made from individual strands of fiber glass. These products contain dedusting oils which are commonly carcinogens.

Unbonded loose fill products are most preferable because they do not contain binder like bonded loose fill products do. See rules of thumb above for tips on how to avoid products made from recycled glass products containing lead.

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. Many products have over 60% post-consumer recycled content and should be preferred.

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.

To avoid these hazards, prefer unfaced batts that use an alternative dedusting oil, such as vegetable oil. See rules of thumb above for tips on how to avoid products made from recycled glass products containing lead.

See New Research Shows Formaldehyde No Longer Used in Residential fiber glass Insulation


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/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 are 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.

Loose cellulose insulation typically contains more than twice as much boric acid flame retardant as cellulose batts - about 15% 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.

As of 2016, HBN was unable to find loose cellulose insulation products on the market that do not contain boric acid.

However, you can make the best selection possible by preferring products made without carcinogenic dedusting oils.

Unlike kraft-faced fiber glass batt insulation, batts faced with PSK (polypropylene-skrim-kraft) and FSK (foil-skrim-kraft) tend to be very poorly disclosed by manufacturers. Like kraft-faced fiber glass batts, these products 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 fibers are made from a molten mixture of rock and blast furnace slag from the steel industry. The fibers are 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 is becoming available without formaldehyde-based resins. Prefer these products when possible or substitute insulation materials higher in this chart. If you must use mineral fiber insulation with a formaldehyde-based binder, prefer those that meet California Emission Specification 01350 requirements for Residential Scenarios.

Fiberglass board insulation is made from a core of fiberglass and typically a formaldehyde-based binder. The core is then covered by densely-packed strands of fiberglass 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, used as a flame retardant in these insulations, is a carcinogen that is also a developmental and reproductive toxicant.

Fiberglass 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 fiberglass board insulation when applicable.

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 chlorinated flame retardant that is considered a very high concern to avoid because of its persistence and toxicity and its ability to migrate from products

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 contains the flame retardant hexabromocyclododecane (HBCD for short) which is highly toxic, persistent in the environment, and bioaccumulative. It also commonly contains an insecticide to make it resistant to termites who might otherwise burrow into it in below-grade installations. This insecticide is known to be hazardous to bees.


Extruded polystyrene is made from the same polystyrene beads as EPS, but the beads are extruded into a solid block. The result is that there are fewer pores between the beads, and therefore XPS is less vulnerable to termites and does not typically contain an insecticide. However, XPS relies on a blowing agent that contributes to global warming. As much as 9% 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. XPS also contains the flame retardant hexabromocyclododecane (HBCD) which is highly toxic.

By 2018, XPS insulation made without HBCD will be available in the US, however, the common replacement flame retardant is still brominated, and there are data gaps in its hazard assessment.

See HBCD-free Styrofoam™ Insulation Coming to USA

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 additives into the surrounding area, exposing installers to these hazardous ingredients. Fumes from the reaction have also been known to ignite and cause explosions.

Additionally, while it is generally thought that after 24 hours, the chemical reaction in the foam is complete, evidence suggests that the time required to fully cure the foam may be much longer, which could potentially expose residents to these same hazardous ingredients.

Isocyanates are asthmagens. The additives typically included in Part B of the foam mixture include a PBT tin catalyst and a chlorinated flame retardant, considered a very high concern to avoid because of its persistence and toxicity and its ability to migrate from products. Closed cell spray foam also uses a blowing agent that is a highly potent contributor of global warming.

Last updated: June 18, 2018