A flame retardant formulation which is the combination of at least (1) at least one bromine-containing polyol flame retardant formed from the reaction of (a) tetrabromophthalic anhydride, (b) an aliphatic polyol, and (c) an epoxide, and (2) at least one aliphatic diester of an alkane dicarboxylic acid, with the proviso that the formulation has a viscosity at 25 C. of about 20,000 cps or less, and a bromine content of at least about 40 wt %. A flame retardant compound formed from A) tetrabromophthalic anhydride; B) diethylene glycol; C) at least one alpha-omega alkane diol, or at least one alpha-omega alkane diol and at least one aliphatic monool; and D) at least one alkylene oxide; with the proviso that the compound has a viscosity at 25 C. of about 60,000 cps or less, and a bromine content of at least about 43 wt %. Polymer compositions formed from (a) a polyurethane or a polyisocyanurate and (b) a formulation of the invention.