An ethylene/vinyl alcohol co-polymer (EVOH) has been chemically modified to induce the formation of ionic clusters. -COOH containing pendant groups have been grafted on the polymer backbone and subsequently have been partially or totally salified. The structure of this class of polymers is expected to be less sensitive to the effect of water vapour if ionic concentration is above a threshold value which guarantees the formation of ionic aggregates. Moreover, the presence of ionic couples should guarantee an increased compatibility towards other polymers if compared to EVOH. Water vapour transport properties of functionalized EVOHs have been determined in order to assess the effect of chemical modifications both on water barrier properties and on sensitivity of polymer structure to sorbed water. Water vapour sorption tests have been performed at 358C at several water vapour activities determining both water sorption isotherms and diffusivities. This is a preliminary study on this new class of materials aimed to assess the possible replacement of EVOH films (or EVOH containing multilayer films) with films based on such polymers (or their blends with other polymers) which should be characterized by a higher resistance to 'retorting' conditions