Reheat additive for carbon black polyester and polypropylene.

A method of forming polypropylene resins or poly (ethylene terephthalate) capable of improved reheat, comprising: adding to the resin from 2 ppm to 50 ppm by weight of carbon black, based on the weight of the resin composition It is including carbon black, carbon black having average particle diameter of at least 200 nm, and the carbon black being a black thermal coal.