A process for the production of a polymeric film comprising a copolyester having an acid component and a diol component, said acid component comprising a dicarboxylic acid and a sulfomonomer containing a sulfonate group attached to the aromatic nucleus of an aromatic dicarboxylic acid, said process comprising the steps of: (i) melt-extruding a layer of said copolyester; (ii) stretching the extrudate in at least one direction; (iii) heat-setting the film by raising the temperature of the stretched film to a temperature T.sub.1 in a first heating zone such that (T.sub.M-T.sub.1) is in the range of from 5 to 30.degree. C., and then raising the temperature of the film to a temperature T.sub.2 in a second heating zone such that (T.sub.M-T.sub.2 is in the range of from 0 to 10.degree. C., wherein T.sub.M is the peak melting temperature of the polymeric film; wherein T.sub.2 is greater than T.sub.1; and wherein the times which a transverse section of the film spends in the first and second heating zones are defined by t.sub.1 and t.sub.2, respectively, such that the ratio of t.sub.1 to t.sub.2 is at least 2:1; and a polymeric film obtainable thereby having an ultimate tensile strength at destruction in the range of 2 to 15 kgf/mm.sup.2 in the machine direction and 2.5 to 17 kgf/mm.sup.2 in the transverse direction.