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The mechanism of flame retardancy and smoke suppression by melamine in flexible polyurethane foam has been investigated using cone calorimetry, TG, DSC and pyrolysis/GC/MS. The cone calorimetric results indicate that the addition of melamine into polyurethane foam was very effective at reducing heat release rates and suppressing smoke and CO production during the initial combustion stage. GC/MS analysis showed that the volatiles evolved from polyurethane foam, pyrolysed at 3508C in air, consisted mainly of the 2,6-and 2,4-isomers of toluene diisocyanate. Such species together with other aromatic compounds are accepted as being the main contributors to smoke released from polyurethane foam in a fire. Cone calorimetry, DSC and pyrolysis/GC/MS experiments indicated that interaction occurs between melamine and the evolved toluene isocyanate fraction arising from the decomposition of polyurethane foam. The resulting polymeric structures so formed will reduce the amount of aromatic smoke precursors evolved thus suppressing smoke in the event of a fire. This polymeric structure will also degrade to a char, reducing the amount of combustibles volatilized and hence the rate of heat release. The char would form a protective layer on the surface of the polyurethane foam. A mechanism for this important melamine-isocyanate interaction is proposed.