A medical probe includes a shaft and an expandable balloon. The shaft is configured for insertion into an organ of a patient. The expandable balloon is coupled to a distal end of the shaft, with the expandable balloon including: (a) an expandable membrane having an outer surface and an inner surface, wherein the expandable membrane is configured to be expanded from a collapsed shape to a balloon shaped member, (b) a plurality of electrodes disposed on the outer surface of the expandable membrane, (c) one or more wires connected to the plurality of electrodes, the wires extending from the distal end to the electrode, (d) and an expandable cover that encapsulates the wires between the expandable cover and the expandable membrane so that the wires are constrained between the cover and the expandable membrane but the electrodes are exposed to ambient environment.