Compositions containing at least about 30% of a poly(alkylene terephthalate), at least about 3% of a polylactone, about 0.05% to about 10% of a carbodiimide and at least about 0.05% to about 10% of an aliphatic phosphite, all percentages being by weight based on the weight of the composition, has excellent thermal stability. The compositions are useful for wire insulation and cable jacketing. Heat recoverable articles, such as tubing and molded parts can be prepared from the compositions.