The present invention provides a co-polymer polyol which has an ABA block structure wherein each A block comprises a plurality of hydroxy-carboxylic acid residues and the B block comprises at least one dimer fatty residue selected from a dimer fatty diacid residue, a dimer fatty diol residue and a dimer fatty diamine residue, wherein the co-polymer polyol comprises at least two hydroxyl end groups. The invention also provides a method of making the co-polymer polyol and a polyurethane comprising the co-polymer polyol.