There is described a composite board comprising: iv) cellulosic plant material; v) a hydrophilic substance; and vi) an adhesive or resin. There is described a method of making a composite board comprising the steps of: i) providing particulate cellulosic plant material; ii) treating the cellulosic plant material with a hydrophilic substance; iii) adding an adhesive or resin to the cellulosic plant material treated with the hydrophilic substance iv) forming a board with the mixture formed in step iii); and v) drying the board.