Pure organic PU foam is typically Class B2 or B1 (GB 8624), with a limiting oxygen index of 22–26%. To achieve Class A non-combustible, a composite flame-retardant system is required: 1) Add inorganic fillers like melamine or expandable graphite to increase LOI above 32%; 2) Use reactive flame retardants (e.g., DMMP) grafted onto the polymer chain; 3) Laminate inorganic fiber mats (e.g., ceramic fiber) on the foam surface as a fire barrier; 4) Encapsulate the core with magnesium cement or magnesium oxysulfate board. Even with these measures, the strictest classification is Class A2 (total heat value ≤3 MJ/kg). Fully inorganic cores (e.g., stone wool) are true Class A1 but have poorer insulation. In engineering, fire-retardant PU sandwich panels are often used as Class B1, supplemented by sprinkler systems to meet codes.
Can the fire resistance rating of rigid PU foam sandwich panels reach Class A? How to improve it?
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