A fluid, polyester insulating composition is made by admixing: (A) about 15 mole % to about 40 mole % of unsaturated cyclic dicarboxylic acid; (B) about 5 mole % to about 20 mole % of an unsaturated aliphatic dicarboxylic acid; (C) about 35 mole % to about 60 mole % aliphatic dihydric alcohol; (D) about 25 mole % to 35 mole % copolymerizable monomer; and (E) an active dual inhibiting agent combination of hydroquinone and mono tert butyl hydroquinone, and up to about 10 parts by weight melamine per 100 parts by weight polyester.