Abstract: Disclosed is a method for fluorinating the surface of a polymeric solid for improving a surface property of such solid while substantially maintaining the bulk physical properties of said solid. This method comprises contacting the polymeric solid with dilute fluorine gas at a temperature not substantially above about room temperature and at a pressure not substantially above about 1 atmosphere for a time adequate to partially fluorinate said solid surface by forming stable fluorocarbon groups wherein the ratio of --CF.sub.2 -- groups to --CHF-- groups is not substantially above about 1:1, the proportion of oxygen-providing groups presend during said fluorination being restricted to an amount whereby substantially no oxidation of said surface occurs.