A new polypropylene terephthalate composition is provided. The polypropylene terephthalate is comprised of 1,3-propanediol and terephthalate. The 1,3-propanediol is produced by the bioconversion of a fermentatble carbon source, preferable glucose. The resulting polypropylene terephthalate is distinguished from petrochemically produced polymer on the basis of dual carbon-isotopic fingerprinting which indicates both the source and the age of the carbon.