Water treeing is an interesting phenomenon, first observed as a degradation mechanism for power cables and currently being used as a unique membrane production methodology. It was discovered that the combination of high electrical field strength with the presence of water and solutes can lead to oxidation reactions creating nanostructured channels in some plastics. In recent years, this process had been recreated and optimized in lab conditions. to the point of reproducible synthesis of thoroughly 'water-treed' foils from cheap base materials (e.g. polyethylene), suitable for use as membranes (Ionomeric High Voltage Membranes). Permeation and ion selectivity have been demonstrated and are optimized further by fine-tuning production parameters and by chemical post-treatment. Among various possible applications being looked into, specific investigations are ongoing towards application in energy generation through reverse electro dialysis ("Blue Energy") and N-2/CO2 separation in power plant flue gasses (e.g. in EU FP7 integrated project NanoGloWa). (C) 2009 Elsevier B.V. All rights reserved.