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Green Building News

Study Details Health Risks of Insulation and Air-Sealing Products

A group of healthy building advocates recommend avoiding spray foam and products containing formaldehyde

A group studying the health implications of using certain building products recommends cellulose and fiberglass insulation over spray foam. (Photo: Dennis Schroeder / National Renewable Energy Laboratory)

A group of organizations promoting energy-efficient housing has published a report on insulation and air-sealing products, concluding that chemical emissions from some commonly used building materials can pose long-term health risks.

A Guide to Healthier Upgrade Materials comes from a group called Energy Efficiency for All and is based on research by the Natural Resources Defense Council, the International Living Future Institute, the Healthy Building Network, and others.

Although written specifically for those working on energy upgrades for affordable multifamily projects, the recommendations should be useful across the building industry, the authors said.

The benefits of insulating and air sealing are clear, the report said, but upgrades also can introduce a variety of chemical hazards, including halogenated flame retardants, formaldehyde-based binders, isocyanates, and phthalate plasticizers.

“The health effects of these chemicals include reproductive and developmental impacts, carcinogenicity, and the ability to cause or exacerbate asthma,” the report notes. “Moreover, some of these chemicals persist and accumulate in the environment and in people and thus can have broad-reaching, long-term impacts.”

The health ranking for various types of insulation and air-sealing products favors fiberglass and cellulose insulation over foam insulation, especially foams that are mixed on site. It also recommends acrylic-based sealants with low levels of volatile organic compounds over modified polymer and polyurethane sealants that typically contain phthalates and other chemicals.

The potential for chemical emissions is key because Americans spend an average of 90% of their time inside, the report says. Chemical components of insulation and air-sealing materials also pose threats to the workers who manufacture, install, and dispose of the products.

Researchers blamed the problem on a weak regulatory environment, misconceptions about chemicals in building products and their impact on health, and a lack of disclosure about chemical content. A 1976 law on toxic substances grandfathered some 62,000 chemicals without any evaluation, for example, and in the 40 years since then the Environmental Protection Agency has required health testing on only about 200 of them.

“Chemicals are assumed safe unless proven otherwise,” the study says. “And even for restricted chemicals the actual restrictions can be minimal.”

Ranking building insulation

The report includes rankings for building and pipe insulation, ranging from the very best to the very worst products on the market. Researchers liked expanded cork board the best, but also included loose-fill fiberglass, dense-pack fiberglass, spray-applied fiberglass and fiberglass batts in the same “green” category.

Also recommended, although not as highly, were fiberglass batts, cellulose and cotton batts, loose-fill cellulose, dense-packed cellulose, and wet-blown cellulose.

At the bottom of the rankings were spray polyurethane foam (the worst) and extruded polystyrene (XPS). In the middle were mineral wool batts and boards, polyisocyanurate, and expanded polystyrene (EPS). Similarly, the report recommends formaldehyde-free fiberglass pipe insulation over polyethylene foam or elastomeric foam pipe insulation.

“Not all products toward the top of the ranking are expensive or limited in availability,” it notes. “Commonly used fiberglass and cellulose insulations are some of the highest ranked from a health perspective, and have the lowest installed cost for any given R-value. While the R-value per inch is higher for many foam products, the R-value per dollar is not.”

Air-sealing products

Air-sealing products that are applied wet emit “chemicals of concern” as they dry or cure, the report says, so solid forms of sealants are usually better choices. General recommendations include:

  • Caulk-type sealants are better than spray-foam sealants.
  • Foam sealing products that are not reacted on site are better than those that are.
  • Avoid products with phthalate plasticizers.
  • Look for acrylic-based sealants with low levels of volatile organic compounds.
  • For HVAC sealing, use foil-backed butyl tape.
  • Avoid products that are marketed as antimicrobial.

The best sealants from a health standpoint were, in order, non-combustible sodium silicate caulk, expanding polyurethane foam sealant tape, acrylic latex sealant, siliconized acrylic sealant, and intumescent acrylic firestop sealant.

The three worst were one-component polyurethane sealant (at the very bottom), one-part polyurethane spray foam sealant, and modified polymer sealant. These contained a variety of chemical components with an impact on health, including organotin catalyst, phthalates, halogenated flame retardant, and isocyanates.

The Environmental Protection Agency also has raised health concerns about spray polyurethane foam and suggests that people with a history of skin conditions, respiratory allergies, or asthma may want to consider alternatives.

How do you know what you’re buying?

The report discusses the potential health consequences of using building products that contain certain chemicals. But the authors acknowledge that it’s not always easy for consumers to know exactly what they are buying.

“Even as we seek safer alternatives to harmful chemicals in building products, we at the same time need content transparency so that we can know what chemicals comprise a given product,” the report says. “Unfortunately, chemical transparency has been difficult to secure. Manufacturers often cite proprietary concerns, face complex supply chains, or simply fail to recognize the need to disclose detailed material information.”

When a number of similar products are on the market, it’s easier to gather information about what’s in them. But it’s more difficult to evaluate a single, “one-off” product when the contents are not fully disclosed. As a result, the report could not recommend some promising products, such as non-isocyanate one-part spray foams.

The authors suggested that the industry take a number of steps, such as urging manufacturers to be more transparent about what goes into their products. Builders also should support the development of healthier products so they get to market as soon as possible, and get involved in industry-wide discussions about the problem.

Once manufacturers see a demand, the authors note, they develop new products that can meet both health and energy performance criteria.

This post was updated with a new photograph on Jan. 3, 2018.


  1. tommay | | #1

    The picture alone with the guy in a hazmat suit should be a dead giveaway......

  2. Jon_R | | #2

    The decline in emissions in a new house is exponential - so there is a lot to be said for not moving into a new house until 30+ days after everything has been completed.

    1. Expert Member
      Dana Dorsett | | #10

      It's not exponential but rather a logarithmic decay. (The rate emission decline slows with time, rather than speeding up.)

      But yes, waiting for the first month or two after the installation probably makes sense.

      1. Jon_R | | #11

        What I wrote is correct (because negative exponents exist). Or call it exponential decay.

      2. Trevor_Lambert | | #12

        Jon is correct. The characteristic of Exponential change is that it changes proportionately to its current value. For positive changes, this means an increase in rate of change over time. For negative changes, it means a decrease in the rate of change over time.

        1. maine_tyler | | #15

          Y'all put me into a math expedition.

          Not that it matters, but...

          Is describing it as exponential (negative) most accurate to describe the decrease of output (where there is no vertical asymptote, as we don't start with infinite output) and describing it as logarithmic would best describe how much total has been emitted (i.e. the concentration level given a completely closed, non-ventilated, accumulating environment)?

          FWIW radio active decay is equated to something like:

          where N(t) is amount at given time, N(o) is initial amount, and k is a constant.

          As I write this I wonder if the off-gassing we are referring to is truly exponential/logarithmic, or if those are just rough terms used to indicate that it has some 'curve' to it... and is not linear...?

    2. schreib77 | | #38

      Jon, . . . man, you really started something. All of us engineers "have to be right" and make sure you know it! For the record: I also use "exponential" both ways-- negative and positive. You made your point simply and succinctly. Period.

  3. Expert Member

    It also makes a great deal of difference where the materials are relative to the air-barrier.

    1. schreib77 | | #39

      Correct Malcolm. Who cares if my sprayed foam is above my home ceiling's sheetrock. Maybe the outgas will kill those dang box elder and lady bugs that get into everything in the fall!

  4. _Stephen_ | | #4

    That's a good point Malcolm. My garage ceiling is spray foamed, but it's on the outside of the air barrier, so there was never any scent inside the house at all. The garage smelled bad for a week though.

  5. AntonioO | | #5

    Can anyone think of a coating that does not include a "chemical of concern" that could be applied to SPF to seal in the compounds that may be offgassed?

    1. Expert Member
      MALCOLM TAYLOR | | #14

      Anything that acts as an air-barrier. Drywall, poly, plywood.

  6. NathanRempel | | #6

    Surprised to see mineral wool falling in the middle here. Its been my preferred batt insulation due in part to my understanding that it is non-carginogenic and offgasses very minimally. Not to mention ease of quality install.
    This is from the European Insulation Manufacturers Association, so bias
    is to be considered, but it seems like a safe product.

    What am I missing?

  7. ONTHEMARK001 | | #7

    So misleading, formaldehyde has been a leading binder in fiberglass batt insulation.
    Spf offgassing primarily occurs when mixing the two components, so ppe is a must but once the spf is manufactured the product chemicals become inert.

    1. Expert Member
      Michael Maines | | #8

      10% of the offgassing occurs at installation; the rest occurs over the lifetime of the product, with up to 50% estimated to remain in the foam cells after 50 years.

      1. Expert Member
        Peter Engle | | #9

        This also assumes that the chemicals are mixed and applied properly. Achieving ideal conditions for chemical manufacturing at a construction site is unlikely, at best.

    2. GBA Editor
      Martin Holladay | | #20

      All fiberglass batts sold in the U.S. have been formaldehyde-free for several years.

  8. canada_deck | | #13

    NathanRempel I haven't read the study but my guess is that it is related to the formaldehyde that has been used in most mineral wool. That said, as of very recently manufacturers are now offering versions that don't have formaldehyde.

  9. maine_tyler | | #16

    "At the bottom of the rankings were spray polyurethane foam (the worst)"

    "The best sealants from a health standpoint were, in order, non-combustible sodium silicate caulk, expanding polyurethane foam sealant tape"

    Something different going on in the tape I guess?

    1. schreib77 | | #40

      NO. It is foamed at the factory and the emissions occur THERE. Any installer won't see it but it happens. The problem is that foam-in-place is MUCH more effective in doing the job than anything else. It will continue to be used regardless, I believe, for that simple reason.

  10. Mikieboy | | #17

    I am about to use Foam It Green brand closed cell foam to insulate HVAC duct and likely areas in the attic and crawl space. This foam claims to be formaldehyde free but does have a mold inhibitor. That said, it seems GBA advocates the use of spray foam, so where does this article leave us?

  11. GBA Editor
    Martin Holladay | | #18

    GBA does not advocate the use of spray foam, but we alert readers to situations where spray foam is one possible solution to an insulation or air-sealing problem. I'm a strong proponent of vented unconditioned attics with cellulose on the attic floor, but GBA readers often ask, "How do I create an unvented roof assembly?" My standard answer is something like, "You have two choices. You can install rigid foam on the exterior side of the roof sheathing, or you can install closed-cell spray foam on the interior side of the roof sheathing."

    For information on foam-free ways to build, see this article: "Building a Foam-Free House."

  12. GBA Editor
    Martin Holladay | | #19

    A general comment on the NRDC paper that Scott is describing: While the paper discusses the chemicals present in the products under discussion, it doesn't really address human health risk. (This is a way of admitting that the GBA headline on this page is somewhat misleading.)

    Some builders may want to take the road suggested by this NRDC paper -- that is, eliminating certain products from the buildings they build. But it should be noted that the dose makes the poison. (A word search for "dose" and "dosage" in the NRDC paper resulted in zero results.)

    If I use a caulk with a troublesome chemical to seal the crack between a window frame and the rough window opening, and then I install drywall window returns, is there reason for me to be concerned about possible health effects to the occupants of the building? I doubt it. Of course, there may be some (limited) risk to the worker installing the caulk -- and that matters -- but this NRDC report doesn't make any attempt to quantify that risk.

  13. JohnP123 | | #21

    Its important to apply some parity here. There is no silver bullet insulating options, they all have the pros and cons. If we are talking about light framed construction that is existing, every detail can be unique and require its own solution(s). SPF is just that, a solution to particular efficiency or hygrothermal concerns. Its not the panacea. Are we supposed to believe the boric acid found in cellulose is not harmful? It is a pesticide. Or how about the mesothelioma potential from fiberglass or rock wool batting chards? These examples aren’t meant to be “negative for a negative”. SPF is not as bad as the article is claiming and cellulose/fiberglass is not as safe as they are claiming. As an installer of all forms of insulation, I constantly need to weigh out the options for clients (and employees) that I present insulating options to. Mold and ice daming issues are call backs that I do not want to deal with – SPF sometimes present the best solution to hygrothermal challanges. Sometimes SPF is the only solution for particular roof details. But it is not the answer for all roofs/attics. Additionally, you cannot conflate raw material health concerns with finished product health concerns. The EPA’s concerns about SPF are specific to worker safety. Ensuring proper installation of SPF is critical to having a good performing finished assembly. The bigger issue here is tending to proper indoor air quality as it relates to tight envelope construction. Virtually everything emits VOC’s (natural or synthetic). The key to all indoor air quality pollution is dilution.

    1. Jon_R | | #26

      > The key to all indoor air quality pollution is dilution.

      I disagree. First is source control, a more expensive/less effective second is dilution. True for chemicals, radon, and even water vapor.

      +1 on the study being nearly worthless - because it doesn't consider the "as used" health effects.

  14. JohnP123 | | #22

    One more thing to add - If your concern is emissions with SPF, I would advise everyone to select products that have green guard certification. Gaco Westerns closed cell system called 'One Pass' is an example: . This is not a pay to pass test.

    1. MattJF | | #28

      I think most people here would be looking to use the GacoOnePass Low GWP, which at this time does not appear to be green guard certified, but it may in process.

      With spray foam, containment while spraying through draping and depressurization are key. Air exchange rates in the near term after spraying makes a big difference. It would be good if installers worked to maximize air exchange while maintaining containment. Setup exhaust fans and then open widows while using a digital manometer to check that there is a few Pa differential with any untreated spaces.

  15. Trevor_Lambert | | #23

    "Are we supposed to believe the boric acid found in cellulose is not harmful?"

    Actually, yes. Unless you have some evidence to the contrary to offer up. Once installed, there is almost zero risk presented. Even during installation, it's been shown to be at most an eye and throat irritant.

    1. Trevor_Lambert | | #25

      Seriously? No one disputes that boric acid, at certain levels, is toxic. Based on this link, I will continue to not eat cockroach poison.

      I could take an ingredient in just about every single building material (and most foods, for that matter) and give you a link saying it's poison.

      1. Expert Member
        Dana Dorsett | | #32

        Ingesting enough water to cause serious life/health risks isn't that hard to do, but we don't require cautionary labeling on bottled water or drinking fountains. (Long distance runners are among the most likely to succumb to hyponatremia due to over-drinking during races in the quest to avoid dehydration.)

        The borate exposure levels experienced by the occupants of homes insulated with cellulose have to be MANY orders of magnitude lower than the exposures of cellulose installers. The installer exposure levels and health effects have been studied by OSHA and other workplace safety regulatory agencies, and the mitigation requirements for installers aren't very stringent at all. For the occupants of those houses the borate in the walls & attic are safer than their uncontrolled water taps capable of delivering many lethal doses per hour.

  16. joshdurston | | #27

    Anyone else notice the bad Photoshop of the repeating stud bays?
    It's hard to un-see once you notice. Some are shifted slightly vertically as you move to the right away from the sprayer but the insulation deformities are consistent.

    1. MattJF | | #29

      Ha! That is pretty bad. Open cell is lively stuff and certainly not that consistent, which is why someone probably didn't like the look of the actual situation.

    2. Expert Member
      MALCOLM TAYLOR | | #30

      Good catch!

      When I see installations like that I can't help imagining how much of the foam ends up as useless waste when it is trimmed flush.

      1. Expert Member
        Dana Dorsett | | #33

        Even with the trim-scrap rate included open cell polyurethane uses less than half the polymer per R of closed cell. Yes, the scrapped foam is a waste, but not nearly the waste that installing closed cell foam between thermally bridging framing is, even at zero scrap rates on the closed cell.

  17. GBA Editor
    Scott Gibson | | #31

    Thanks, Josh.

    The photo has been replaced.

    1. joshdurston | | #34

      Cheers, I wasn't really complaining... just marveling at it.

  18. JohnP123 | | #35

    Trevor: "I could take an ingredient in just about every single building material (and most foods, for that matter) and give you a link saying it's poison." Bingo. I couldn't agree more. Look, I am neutral in my perception of cellulose. I have some clients that love it, some clients hate it. To me, its another arrow in the quiver for me to make buildings more efficient and code compliant. I am simply trying to provide some context to perceived issues with different types of insulation.
    Jon R: Source control is an absolute must. However, if we're committed to building tight, unless we want to create surgical grade indoor environments, with no consumer goods or people habitation, we still need to dilute. Regarding your concerns with water vapor, I envision a day where dehumidification will be code required in tight enveloped construction.

    1. Expert Member
      MALCOLM TAYLOR | | #36


      We have had that in our code here in BC for about a decade. Every house had a humidistat linked to the bathroom exhausts. Our recent code requirements for full-time mechanical ventilation have superseded it.

  19. AndyKosick | | #37

    I was going to say this last but I'm going to say it first:

    The most important thing this report does is call for our industry to demand better, less toxic materials to work with.

    The report provides good perspective but has to viewed in the light of other criteria. It's an important reminder that we are trying to protect both people and environment. Trading energy consumption for toxic chemical exposure doesn't make sense but it something our industry is at risk of. That said, the report does not talk about dosage or if the chemicals in the products are actually getting to people from these applications.

    There's a couple of things I found in there that speak to the limitations of this report. First, "Prefer metal weatherstripping". I completely understand why metal has the least chemicals but "prefer" and "metal weatherstripping" are words I never thought I'd see in the same sentence. I don't see may people choosing this. I also realized I've retrofit quite a few doors with silicone bead weatherstrip and that wasn't mentioned at all. Second, and maybe I'm wrong, but "Expanded Cork" doesn't seem like it could be scaled to meet the demands of the insulation industry and its current market without creating environmental problems akin to palm oil.

  20. user-7182669 | | #41

    Does anyone have any experience/comments on the use of AirKrete. I have an area that needs insulation on a steep pitched roof. There’s a barrel ceiling I can get to insulate but there is 7’ on both sides that is part of ceiling and roof on the outside separated by rafters. The space I’m looking to fill is 3” x 12” x 7’ deep. I’m going for an R60 on the ceiling. Any advice/recommendations would be helpful and appreciated. Thanks

    1. GBA Editor
      Martin Holladay | | #42

      User 7182669,
      First of all, can you tell us your name? (I'm Martin.)

      Here is a link to a Q&A thread that discusses Air Krete insulation: "Air Krete."

      1. user-7182669 | | #43

        Thank You Martin for the link to the Air Krete, I’ll check that out. My name is Dan Schwartz.

  21. dan7210329 | | #44

    Link at beginning of article, "A Guide to Healthier Upgrade Materials" is broken. I found list starting page 30 of downloaded pdf at
    (Hope this helps, but sorry if this is a redundant post)

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