Abstract: A concentrate composition, that can be diluted with water to form an aqueous size for cellulosic fibres, comprises a substantially anhydrous dispersion of polyelectrolyte particles in a non-aqueous liquid comprising a reactive size, and is made by forming a dispersion in a hydrophobic liquid of the polyelectrolyte particles while they are swollen by water, azeotroping the dispersion and adding the size to the hydrophoboic liquid. If the size is a liquid size, the hydrophobic liquid may be removed from the composition. The dispersion of swollen polyelectrolyte particles in the hydrophobic liquid can be amde by dispersing a solution of polyelectrolyte in the liquid but is preferably made by reverse phase polymerization.