A thermoplastic resin containing a flame-retarding magnesium hydroxide has its workability enhanced by a sorbitan ester in admixture with the resin and flame retardant. An admixture of the resin, magnesium hydroxide, and ester may be either a mixture of discrete particles of each of said components of the composition or a mixture of the resin and a magnesium hydroxide powder whose particles have a coating of the ester.