The present invention relates to polyester polyols made from aromatic polyacid sources such as thermoplastic polyesters. The polyols can be made by heating a thermoplastic polyester such as virgin polyethylene terephthalate, recycled polyethylene terephthalate, or mixtures thereof, with a glycol to give a digested intermediate which is then reacted with a digestible polymer, which can be obtained from various recycle waste streams. The polyester polyols comprise a glycol-digested polyacid source and a further digestible polymer. The polyester polyols provide a sustainable alternative to petrochemical or biochemical based polyester polyols.