Abstract: A smoke suppressant for reducing smoke emission when a flammable organic material is heated above its decomposition temperature or ignited comprises a liquid heterocyclic polysulphide compound having the formulaR--S.sub.x --Z--S.sub.x' --R' (I)where R is an organic group containing 1 to 12 carbon atoms, R' is hydrogen or an organic group containing 1 to 12 carbon atoms, x is at least 2, x' is 1 or more when R' is hydrogen and is at least 2 when R' is an organic group and Z is a divalent radical derived from a heterocyclic compound, preferably a sulphur-containing heterocyclic compound such as thiadiazole. The compound (I) may contain dissolved or dispersed elemental sulphur. The smoke suppressant is particularly suitable for use in polyurethane foams.