Abstract: A method for maintaining pore size of a reusable filtration membrane, said method comprising exposing said filtration membrane to a plasma comprising a hydrocarbon or fluorocarbon monomer so as to form a polymeric layer on the surface thereof. The treatment allows the filtration membrane to withstand washing procedures, in particular caustic washing. Thus reusable filtration membranes treated in this way and their use, form a further aspect of the invention.