Baybond PU 401 Polyurethane polymer Bayer MaterialScience Polyurethane (PU) - Polyurethane dispersions (PUDs) >> Polyester Solvent free, polyurethane dispersion (PUD) in water. Commonly used as the film-forming component in glass fiber sizing. Glass fiber sizes based on Baybond PU 401 polyurethane dispersion have excellent film-forming properties and very good adhesion. As with any product, use of Baybond PU 401 polyurethane dispersion in a given application must be tested (including but not limited to field testing) in advance by the user to determine suitability. Polyurethane dispersion. Offers very good film-forming properties and very good adhesion.