Sealant Hazard Spectrum
The Healthy Building Network has researched a variety of sealant products, and we rank these products on a simplified spectrum below. Products in the green categories are better options than those that appear 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.
Compared to some other types of building products, the compositions of sealant products are poorly disclosed. Encourage manufacturers to fully disclose the content and associated health hazards of sealants through the industry’s collaborative, user-designed open standard, Health Product Declaration (HPD). This information is particularly needed for non-isocyanate spray foam sealants so they can be vetted as potentially healthier options compared to standard spray foam sealants.
Here are some general rules of thumb to use when choosing a sealant product:
Avoid hazardous phthalates. In some categories of sealants, phthalate plasticizers are still used. Many phthalates are known endocrine disruptors and have been found to damage reproductive systems and interfere with the normal development of a fetus in the womb. They have also been associated with asthma.
Prefer caulk-type sealants to spray foam sealants. Most spray foam sealants contain asthmagenic isocyanates along with other chemicals of concern.
If foam sealing products are needed, prefer those that are not reacted on site, like foam sealant tape, instead of a spray foam sealant.
For a multi-purpose sealant, absent full disclosure, look for acrylic-based sealants with very low VOCs - options with ≤ 25 grams per liter (g/L) are available for many applications.
Note that many standards call for sealants that meet the requirements of the South Coast Air Quality Management District (SCAQMD) Rule 1168. For architectural sealants, however, this limit has been very permissive, allowing up to 250 g/L VOCs. Products with significantly lower VOC content are available for air sealing applications. A new version of SCAQMD Rule 1168 was released last year and much more restrictive requirements (≤ 50 g/L for most architectural sealants) go into effect January 2019.
- Avoid products that are marketed as being antimicrobial or claim to kill germs on the surface as they have not been shown to have a health benefit, and can have negative impacts on human health and the environment.
For some applications, sealants may need to have certain flammability or fire resistance ratings including Class A, fireblock (ASTM E136), or firestop (ASTM E814). Within the spectrum below, there are options for fireblock sealants (non-combustible sodium silicate) and firestop sealants (acrylic firestop), and some acrylic latex sealants are Class A rated. Not all sealant products are recommended for all sealing applications. For example, sodium silicate caulk is a good option from a health perspective, but is not not recommended where there is continuous vibration or in areas expected to come into contact with water. Check with specific product manufacturers for information on flammability ratings of their products and other product performance questions.
Non-combustible sodium silicate caulks are single component, non-intumescent mortar-type caulks. They can be used as a draft, smoke, and fireblocking sealant for penetrations around ducting and electrical and plumbing penetrations. Sodium silicate caulks appear to be free of chemicals of concern, giving this sealant type a green rating.
Expanding polyurethane foam sealant tape is a compressed tape of polyurethane foam. Since the foam is factory-formed, it does not react on-site. Small quantities of PBTs or monomer residuals (including respiratory hazard isocyanates) may be present in the finished product. The low density of this product and the fact that it does not react or dry on-site keeps the quantity of hazardous chemicals in this product low and gives it a yellow rating.
Though not common, some products may contain a chlorinated paraffin flame retardant or an organotin catalyst, both of which are PBTs. Hydrofluorocarbons (HFCs), which have high global warming potential, can also be used as supplemental blowing agents. Avoid these chemicals when using this type of product. At minimum, require the manufacturer to disclose the identity of any flame retardants used.
Acrylic latex sealants are water-based and non-reactive when installed. The primary components of these sealants are non-hazardous, however, some common additives have associated health hazards (such as ethylene glycol, used as an anti-freeze agent, which is a reproductive and developmental toxicant, and organic solvents which can have multiple associated hazards).
While acrylic sealants do contain some chemicals of concern, they do not generally contain PBTs or phthalate plasticizers, and there are options with very low VOC content, giving this category an orange rating.
Note that while the majority of acrylic latex sealants have transitioned to less hazardous dibenzoate plasticizers, some may still contain phthalates. Select phthalate-free products by requiring the manufacturer to disclose, at minimum, the type of plasticizers used.
Also, look for products without the hazardous anti-freeze agent, and with low VOC content, ≤ 25 g/L.
Siliconized acrylic sealants are a variation of standard acrylic latex sealants. In these formulations, manufacturers add small proportions of silicone fluid or silanes to enhance adhesion under wet conditions. Like standard acrylic latex, and unlike silicone sealants which are chemically cured, siliconized acrylic sealants cure from evaporation of water. There is minimal disclosure of the preservatives or surfactants used; a hazardous biocide and octylphenol ethoxylate surfactant may be common. Octylphenol ethoxylates are part of the alkylphenol ethoxylate (APE) chemical group, which are a priority to avoid. See our blog post on APEs in paints for more information.
As with acrylic latex sealants, look for low VOC products and make sure that the products you use are phthalate-free.
Intumescent acrylic firestop sealants are similar to other acrylic sealants, but contain filler materials that react and expand when exposed to very high temperatures. These specialty products are used to seal joints and fill voids around penetrations in fire-rated assemblies to prevent the spread of smoke and fire. There is minimal disclosure of the preservatives or surfactants used; a hazardous biocide and octylphenol ethoxylate surfactant may be common. Octylphenol ethoxylates are part of the alkylphenol ethoxylate (APE) chemical group, which are a priority to avoid. See our blog post on APEs in paints for more information. Zinc borate is also a common flame retardant included in these sealants. Though borate-based flame retardants are less of a concern than halogenated flame retardants, they are emerging chemicals of concern.
Look for low VOC acrylic firestop sealants with low hazard alumina trihydrate instead of zinc borate flame retardants. While not common, some of these products may contain phthalate plasticizers. Make sure products you use are phthalate-free.
One-component silicone sealants cure upon application in the presence of moisture. Volatile methylated siloxanes, like D4, are the key components to silicone chemistry. D4 and an arsenic-based biocide, both chemicals of high concern as PBTs, are common in silicone sealants. In addition, the most common type of systems are "neutral cure" which release a carcinogen, methyl ethyl ketoxime, as they react. Because PBT volatile methylated siloxanes are key to the chemistry of silicone sealants and are typically present at about one percent in the product, these sealants are ranked lower than acrylics.
If silicone sealants must be used, avoid formulations with organotin catalysts (PBTs) or hazardous solvents.
Silyl-terminated polyether sealants are single-component, moisture-cured sealants. These sealants can be referred to as hybrid or modified polymer sealants. They are often touted as environmentally-friendly, being free of solvents and isocyanates; however, hazardous phthalate plasticizers and PBT organotin catalysts are still common. Many phthalates are known endocrine disruptors and have been found to damage reproductive systems and interfere with the normal development of a fetus in the womb. They have also been associated with asthma. Methanol, a developmental and reproductive toxicant, is a product of the crosslinking reaction and is emitted during cure.
The organotin catalysts and around 15% phthalates give these sealants a dark red rating, but since there are better options within this category, it is bumped up slightly. If using a modified polymer sealant, specify those that have fully disclosed contents and use alternative plasticizers like polypropylene glycol which are low hazard.
One-part polyurethane spray foam products come in many varieties for specific applications, but they are relatively similar chemically. They are reacted on-site and may release significant quantities of hazardous volatile chemicals like isocyanates. Isocyanates are a leading cause of work-related asthma, and anyone installing reactive sealants based on isocyanate chemistry may become exposed by touch or breathing. The chlorinated flame retardant, TCPP, is also common and is a very high priority to avoid because of its persistence and toxicity and its ability to migrate from products.
Fireblock one-part spray foam products also commonly contain chlorinated paraffins which are developmental hazards. Carbon tetrachloride is sometimes used in the manufacture of chlorinated paraffins and may be present as a residual. Carbon tetrachloride depletes the Earth’s protective ozone layer and is a global warming agent and carcinogen.
One-part firestop versions additionally contain HFC-134a, a potent global warming agent.
The large percentage of chlorinated compounds, about 11-20%, and the potential for harm from reactive isocyanates on-site, gives one-part polyurethane foam sealants a low ranking. The low density of these products (less chemicals used for a given area sealed) moves them up slightly from dark red.
One-component polyurethane sealants cure with moisture in the air when applied. The isocyanates TDI and MDI can both be included as reactants for this type of chemistry. Isocyanates are a leading cause of work-related asthma. Hazardous solvents are also common in these sealants. There is limited disclosure on the plasticizers and catalysts used, but hazardous phthalates and PBT organotin catalysts are believed to be common. The large quantity of chemicals of concern in these sealants result in the lowest rating.
 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.
 “South Coast Air Quality Management District (SCAQMD) Rule 1168. Adhesive and Sealant Applications,” October 6, 2017.
Foam sealants and foam insulation sealants are still allowed up to 250 g/L VOCs until 2023, and “Clear, Paintable, and Immediately Water-Resistant Sealant” is allowed up to 380 g/L VOCs.
 HomeFree. “New Report on Antimicrobial Building Products: Avoid Whenever Possible.” March 15, 2017.
 US EPA, OCSPP. “Health Concerns about Spray Polyurethane Foam.” Overviews and Factsheets. Accessed February 6, 2017.
 “TSCA Work Plan Chemical Problem Formulation and Initial Assessment: Chlorinated Phosphate Ester Cluster Flame Retardants.” US EPA, Office of Chemical Safety and Pollution Prevention, August 2015.
 “Chlorinated Paraffins: A Status Report.” CPIA: Chlorinated Paraffins Industry Association. Accessed February 2, 2017.
 Soudal Accumetric, Boss 813 “The First” Expanding Firestop Foam (Safety Data Sheet), December 18, 2015,
http://www.accumetricinc.com/uplimg/boss/MSDS/BOSS%20813%20(12-18-15).pdf.; Abesco Fire LLC, Abesco FP200 FR Foam (Safety Data Sheet), August 12, 2015, http://www.fp200abesco.com/downloads/FP200_FR_Expanding_Foam(MSDS006).pdf.
 US EPA, OCSPP. “Health Concerns about Spray Polyurethane Foam.” Overviews and Factsheets. Accessed February 6, 2017.
Last updated: July 16, 2018