Baybond PU 239 Polyester urethane polymer Bayer MaterialScience Polyurethane (PU) - Polyurethane dispersions (PUDs) >> Polyester Anionic/non-ionic crosslinkable polyester urethane polymer based on aliphatic isocyanates. Baybond PU 239 is particularly well suited for the sizing of glass fibers used for the manufacture of thermoplastics, particularly polyamide. With the proper formulation, Baybond PU 239 is also suitable for the sizing of glass fibers used to reinforce thermosets. Glass fiber sizes based on Baybond PU 239 are characterized by their good film-forming properties and adhesion. Polyester urethane polymer based on aliphatic isocyanates. Possesses good film-forming properties and adhesion.