A Wearable Cardioverter Defibrillator (WCD) system comprises an electrode assembly with a permeable ECG electrode and a moisture barrier. In some embodiments, the moisture barrier is configured to reduce drying out of the permeable ECG electrode to improve performance of the WCD system. In a further enhancement, some embodiments of the electrode assembly also include a pillow structure positioned on a non-skin-contacting surface of the electrode assembly to comfortably reduce movement artifact or noise in the received ECG signal.