Improved binder technology for use with fibrous materials is provided whereby the adjoining fibers of a fibrous material are bound in the absence of a phenol-formaldehyde reaction product. A curable binder composition is provided which comprises a water-soluble Michael adduct crosslinking agent having reactive hydroxyl end groups and a polycarboxylic acid capable of undergoing an esterification reaction. The binding composition is coated on a fibrous material and is heated to achieve crosslinking of hydroxyl end groups of the Michael adduct and carboxylic acid groups of the polycarboxylic acid via an esterification reaction to form a cured water-resistant binder in association with the fibrous material wherein adjoining fibers are bound at cross-over points.