A method of manufacturing a cellulosic sheet having at least one of hydrophobic and oleophobic properties comprises the steps of depositing a stock of cellulosic fibres onto at least one forming fabric at an impingement zone and forming a web therefrom in a formation process; combining a water-based composition comprising an adhesion promoter, an organic nanoparticulate polymer and a fluorocarbonwith the web at a preselected combination stage prior to a heating stage at which the web is subjected to a temperature exceeding 60 DEG C; and heat-curing the composition with the web during a drying process. A water-based composition for imparting at least one of hydrophobic and oleophobic properties to a cellulosic sheet during manufacture comprises an adhesion promoter, an organic nanoparticulate polymer and a fluorocarbon. A cellulosic sheet or layer thereof has at least one of hydrophobic and oleophobic properties. Improved resistance of cellulosic sheets to oil or water is obtained.