Abstract: Ion exchange fibers having a thickness of about 2-200 micrometers and a length more than twice the thickness are mixed as a slurry of cation, anion or mixed cation and anion exchange fibers, with or without powdered ion exchange resin of 2-250 micrometers diameter, to intertwine the fibers and immobilize any powdered resin present; the resins are coated from the slurry as a mat on to a filter support; liquids to be purified are passed through the mat until the ion exchange materials are exhausted; and the exhausted mat is stripped from the filter support by a backwash of liquid, gas or both.