Safer Choice

Chemicals and Production of Spray Polyurethane Foam - Why It Matters

This page describes the chemicals and process that produce spray polyurethane foam, how those may affect potential exposures and health and environmental effects. 

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Methods of creating the final products and potential exposures

To create the final SPF insulation or sealant product, a chemical reaction of 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. 

Chemicals in SPF products leave the gun, nozzle, or straw and form a foam as the chemicals react. This chemical reaction generates heat through an exothermic reaction. High-pressure SPF systems may also be applied through heated hoses, increasing the potential for exposure to aerosols and vapors.

The chemical components, particularly isocyanates, and related hazards are similar for the various types of SPF products on the market. However, the amount of product used, the delivery mechanism, and overall application process differs for each type of SPF product; therefore, the potential for exposure may vary, though there is potential for eye, skin, and inhalation exposure to hazardous chemicals with all types of SPF products.

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Chemicals in SPF products

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
  • Other chemicals

Industry is supporting development of a standard method for measuring off-gassing of volatile chemicals.

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Isocyanate compounds commonly used in SPF and related products

Isocyanates are chemical substances containing an isocyanate (-N=C=O) functional group. Diisocyanates have two isocyanate functional groups. Other isocyanates contain several isocyanate groups.

The most common isocyanate compounds used in SPF are listed in the table below. SPF contains MDI and MDI-based polyisocyanates. Other isocyanate oligomers may also form during a chemical reaction. There are numerous chemical names and synonyms for members of the class of isocyanates and the list below is not all-inclusive.

Isocyanate compounds used in SPF.
Chemical Name CAS Number
4,4'-Methylene diphenyl diisocyanate (MDI) 101-68-8
Polymeric Diphenylmethane Diisocyanate (pMDI) 9016-87-9
Diphenylmethane Diisocyanate Mixed Isomers 26447-40-5
2,4'-MDI 5873-54-1
2,2'-MDI 2536-05-2
Generic MDI 26447-40-5
4,4'-MDI homopolymer 25686-28-6
Generic MDI homopolymer 39310-05-9
4,4'-MDI dimer 17589-24-1
Uretonimine of 4,4'-MDI 31107-36-5
4,4'-MDI/ 2,4'-MDI copolymer 109331-54-6

Polyurethane production, which covers a broad area of applications and products, in the United States was estimated at 5.5 percent growth from 2010-2012. In 2012, U.S. demand for all diisocyanates, as a raw material in the production of polyurethanes, was 2,305.2 million pounds, while the demand for use of polymeric MDI in rigid foam, which is used in a range of end-use applications including spray polyurethane foam, was 878.5 million pounds.*

The most widely used isocyanates are:

  • Methylene diphenyl diisocyanates (MDI)
  • Toluene diisocyanates (TDI)
  • Hexamethylene diisocyanates (HDI)
  • MDI-, TDI-, and HDI-based isocyanates

Isocyanates have a broad range of uses in the manufacture of consumer products, including:

Spray applications of isocyanates may generate aerosols, mist, and vapors that can be inhaled or come in contact with the eyes or skin. Potential exposures may occur through skin contact or inhalation of particulates and dust particles containing isocyanates.

*2012, Center for the Polyurethanes Industry, End-use Market Survey Exit

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