Abstract: A fire retardant system useful in a thermosetting resin system comprises a dispersion of particles of a halogen-containing organic material and an inorganic synergist in a liquid phosphorus carrier. The particles in the blend are reduced to 20 microns or less by suitable means, for example, by processing through a 3-roll mill. The composition is incorporated into the resin in an amount of between 3% and 15% by weight of resin where the dispersion remains in suspension during curing of the resin. The thermosetting resin is a saturated or an unsaturated resin such as a polyester, a polyepoxide or a polyurethane. The resin when formed into a ceiling panel has a flame-spread index less than 25 and a smoke rating of 450 or less when tested according to ASTM Test E-84.