Baybond PU 400 S Polyester urethane polymer Bayer MaterialScience Polyurethane (PU) - Polyurethane dispersions (PUDs) >> Polyester Anionic/non-ionic polyester urethane polymer. It is used as the film-forming component in glass fiber sizes. Baybond PU 400 S is particularly well suited for the sizing of glass fibers used to reinforce thermoplastics, particularly polyamide. Glass fiber sizes based on Baybond PU 400 S are characterized by their outstanding film-forming properties and very good adhesion. They have high colorfastness, even at elevated temperatures. Baybond PU 400 S is also stable against shear forces. Polyester urethane polymer. Possesses good film-forming properties and adhesion.