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Safe Use of Spray Polyurethane Foam (SPF)

Spray Polyurethane Foam Project IconSpray polyurethane foam (SPF) is a widely used and highly-effective insulator and sealant; however, eye, skin, and inhalation exposures to its key ingredient, isocyanates , and other chemicals in SPF products of concern in vapors, aerosols, and dusts during SPF installation can cause asthma, lung damage, respiratory problems and other breathing difficulties, skin and eye irritation, or other potential adverse health effects.

To create the final SPF insulation or sealant product, a chemical reaction of two component parts has to occur. Chemicals in SPF products leave the gun, nozzle, or straw and form a foam as the chemicals react. Safe work practices should be in place to avoid exposure at every stage of SPF installation:

Avoid Exposure at Every Stage of SPF Installation


  • Make sure the raw chemical ingredients are handled and stored properly at all times before use to avoid chemical exposure.
  • Read the manufacturer’s label and material safety data sheet (MSDS). Follow the directions to achieve consistent curing conditions and times. Be prepared to carefully manage temperature and other area conditions while the SPF dries or cures. Unpredictable or uncontrolled curing rates can increase the risks of exposure.
  • Make sure workers understand ahead of time how to safely handle chemicals, understand the dangers of exposure, and have the appropriate protective equipment on hand.

Spraying, streaming, or beading application process

  • Avoid exposure to vapor, mist, particulates and dust. Make sure workers wear protective equipment (gloves, respirators, etc.) and chemical-resistant clothing at all times.
  • Ventilate the work area.
  • Isolate the work site and clean up thoroughly, to prevent isocyanates and other chemical vapors from spreading to other rooms or floors. Clean before allowing other unprotected workers or building occupants back into the area.

Trimming of foam

  • Avoid exposure to dust and particles that may contain isocyanates. Make sure workers wear personal protective equipment while cutting and scraping foam.

Clean up after preparation, application, and trimming

  • Clean the work site thoroughly, to avoid exposing other workers and building occupants to dust and particles that may contain isocyanates.
  • Remove protective clothing and handle with care to avoid exposing yourself and others to toxic chemicals.

Long-term Concerns for Exposure Potential
After spray foam is applied and cured, it is considered to be relatively inert; however, there are several situations where the cured foam may pose additional potential risks. (Note: “curing” of SPF means that the chemicals in the product are reacting to produce polyurethane foam; manufacturers estimate 23-72 hours for the foam to fully cure for the two-component high pressure "professional" SPF system, and 6 to 12 hours to cure for one component foam, typically available in 12 oz. to 24 oz. cans.)

  • Maintenance workers, including plumbers and electricians, should not heat or grind spray foam. Spray foam can potentially generate toxic emissions under these circumstances.
  • Building renovations, demolition, or building disassembly done years later can disturb spray foam insulation. Performing hot work on or near polyurethane foam may lead to potential exposures to isocyanates and other toxic emissions.

Chemicals in SPF Products
In order to create the final SPF insulation or sealant product, a chemical reaction of the two component parts, commonly referred to as Side A and Side B, has to occur. SPF products contain approximately 50 percent Side A and 50 percent Side B. This chemical reaction generates heat.

Side A contains very reactive chemicals known as isocyanates. Side B contains a polyol, which reacts with isocyanates to make polyurethane, and a mixture of other chemicals, including catalysts (which help the reaction to occur), flame retardants, blowing agents and surfactants.

Side A contains isocyanates:
  • 4,4' Methylene diphenyl diisocyanate, CAS #101-68-8
  • Polymeric MDI,  CAS # 9016-87-9
  • Generic MDI mixed isomers, CAS #26447-40-5
  • Other similar isocyanates
Side B contains a blend of proprietary chemicals that provide unique properties in the foam, including:
  • Polyols (derived from petroleum and agricultural sources)
  • Flame retardants
  • Blowing agents
  • Amine or metal catalysts
  • Surfactants

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Types of SPF Products and Applications
There are three main types of SPF products.

Two-component “Professional” High-Pressure System:

  • Used for larger insulation applications
  • 55 gallon drum containers
  • Sides A and B are pumped through heated hoses from supply tanks into a nozzle where the two components react and are spray applied at elevated temperatures (>150°F) and pressure
    (1200 psi)
  • After the foam is applied, has expanded, and has cured, it may be trimmed or cut, as needed; this might especially be true for the use of “open” cell foam that may expand beyond the wall.
  • Manufacturers estimate that it can take 23 to 72 hours after application for the foam to fully cure for the two-component high pressure "professional" SPF system.
  • Various products available: “open” cell foam (expands more vigorously) and “closed” cell foam (expands less and may be applied in layers). See photographs below illustrating expansion differences between open-cell and closed-cell SPF.
  • Foam can expand up to 120 times its original volume
Photo showing open-cell foam expanding beyond the 2x4 of the wall.   Photo showing closed-cell foam expanding up to the 2x4 of the wall.
Open-Cell SPF Two-component “Professional” High-Pressure System:
- Low Density
- Expands aggressively
- Dries soft
- Lower R-value (~ 3.5 per inch)
*Photo Courtesy CertainTeed
  Closed-Cell SPF Two-component “Professional” High Pressure System:
- High Density
- Expands less aggressively
- Dries rigid
- Higher R-value (~ 6.5 per inch)
*Photo Courtesy CertainTeed

Two-component Low-Pressure “Professional” and “Do-it-Yourself” Kits:

  • Used for air sealant, adhesive, and smaller insulation applications
  • Typically three to five gallons per container, but can be purchased in larger containers over the internet or in some retail markets
  • Used by professionals for smaller jobs as well as the do-it-yourself applicator
  • Sides A and B combined at application site and sprayed on as a stream or bead
  • After the foam is applied, has expanded, and has cured, it may then be trimmed or cut, if needed
One-component Foam (OCF) Pressurized Cans or Canisters:
  • Used for smaller applications as sealant for filling cracks, holes, gaps, and crevices
  • Available in retail and hardware stores nationwide in a variety of sizes ranging from 12 oz. to 24 oz. cans
  • Used by professionals as well as do-it-yourself applicators
  • Sides A and B are combined in one container by the manufacturer off-site and the reaction of the two components is completed with ambient moisture at the time of application (moisture cured)
  • Manufacturers estimate that it can take 6 to 12 hours to cure for one component foam, typically available in 12 oz. to 24 oz. cans.
  • Applied as stream or bead
  • OCF may be trimmed or sanded
  • Professional applicators are finding more application uses for OCF installation:
    • Around windows and doors
    • For sound proofing
    • For sealing up small gaps (0.5" - 3") in a building to create an energy efficient building envelope

SPF material is highly adhesive and will stick to most surfaces. SPF may appear hardened or "tack-free" within a range of a few seconds to a few minutes after application.  However, at this stage, the interior of the foam is still curing and still contains unreacted SPF chemicals. Manufacturers estimate that it can take 23-72 hours after application for the foam to fully cure for the two-component high pressure "professional" SPF system, and 6 to 12 hours to cure for one component foam, typically available in 12 oz. to 24 oz. cans. Read the manufacturer’s recommendation for this and other types of SPF products and applications in the material safety data sheet and other product information. The curing time (complete reaction) varies depending on the product formulation, applicator technique, foam thickness, temperature, humidity and other factors. Cutting or trimming foam before it is fully cured may cause exposure to unreacted SPF chemicals.

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