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SPF Chemicals

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

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

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.

There is concern for exposure to any isocyanate-containing material related to SPF use, including products that contain only a single isocyanate. It is important to understand the other products that contain isocyanates because if sensitized to isocyanates, even low concentrations of isocyanates can trigger a severe asthma attack or other lung effects, or a potentially fatal reaction.

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

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Chemical Name

CAS Number

4,4'-Methylene diphenyl diisocyanate (MDI)


Polymeric Diphenylmethane Diisocyanate (pMDI)


Diphenylmethane Diisocyanate Mixed Isomers






Generic MDI


4,4'-MDI homopolymer


Generic MDI homopolymer


4,4'-MDI dimer


Uretonimine of 4,4'-MDI


4,4'-MDI/ 2,4'-MDI copolymer


The world production-volume of isocyanates Exit EPA Disclaimer is estimated to be in excess of six million tons annually with growth of 10 to 15 percent annually.  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.

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