through such a treatment of particles or groups of particles such as fibers it is possible to make new types of surface modifications to them by for example treating fibers with consecutive layers of hydrophobic charged polyelectrolytes it would be possible for example to develop new types of hydrophobizing chemicals for the hydrophobization of paper it would also be possible to build up u201c intelligent u201d surface layers on fibers which alter the properties with temperature ph salt content etc these changes could for example be based on fundamental knowledge about modern theories on interaction between polymers and surfactants further applications are ion exchanging fibers where u201c membranes u201d with ion exchanging properties are provided on the fiber surface wet strength agents where the added polymers are reactive with the fibers and with each other in order to provide permanent bonds between the fibers and for the production of highly swelling surface layers where the added chemicals form swollen gel structures on the fiber surface for use in absorbent hygiene products another possible application are new types of fibers for printing paper where the adsorbed polymers change colour when they are exerted to an electric magnetic or electromagnetic field such polymers are available today the fibers that are treated with the method according to the invention can be of optional kind.