Flame-retardant polyurethane compositions

A fabric-reinforced substrate comprising a chain extendable crosslinkable polyurethane prepolymer and

• (a) about 10 to about 50 parts by weight per 100 parts by weight of polyurethane of an organic additive selected from the group consisting of chlorine-substituted and bromine-substituted aliphatic, aromatic, alicyclic and mixed hydrocarbyl compounds having a halogen content in the range of about 35 to about 80 weight percent and optionally containing oxygen substituents in the form of hydroxyl, anhydride, ether, ester or amide groups and which are substantially non-volatile, stable and non-reactive toward said polyurethane and any auxiliary ingredients of said composition at the curing temperature of said polyurethane, and mixtures thereof;
• (b) about 1 to about 10 parts by weight per 100 parts by weight of polyurethane of an antimony compound selected from the group consisting of the antimony oxides, sulfides, salts of the alkali metals of Group I of the Periodic Table, and salts of organic acids and their pentavalent derivatives, esters of antimonius acids and their pentavalent derivatives, cyclic antimonites, the oxides of arsenic and the oxides of bismuth;
• and
• (c) about 3 to about 40 parts by weight per 100 parts by weight of polyurethane of a C.sub.1 to C.sub.5 hexaalkoxymethyl melamine.