Spray foam is formed by chemical reactions between the A and B side materials. These reactions generate heat (exothermic heat) that raises the internal temperature of the foam during the application process. The peak exothermic temperatures of closed-cell spray foam occur at the center of the pass are typically between 225°F to 350°F when sprayed at the manufacturers maximum pass thickness.  When the manufacturer’s maximum pass thickness is exceeded, the peak exothermic temperature increases beyond this range.  

 

Increased exothermic temperatures can cause scorching or mild charring of the foam that can result in poor foam quality. Elevated exothermic temperatures from spraying thick lifts can also damage thermoplastic wiring and piping.  In extreme cases, the exothermic temperatures can exceed 450-500F, which is above the ignition temperature of the foam or substrate and the foam will ‘self-ignite’ - with serious consequences.   

 

It’s important to (1) follow manufacturer’s installation instructions in regard to maximum pass thickness and (2) allow sufficient cooling time between passes. This is especially critical for newer high-lift closed-cell foams which reportedly have higher peak exothermic temperatures.  

Questions?? - Please contact info@sprayfoam.org