A monitor comprises circuitry to receive a signal and process the signal to monitor at least one characteristic of a subject, and a flexible polymer casing forming a waterproof enclosure for the circuitry. The flexible polymer casing is infused with a conductive material at location to form infused electrode that extends from an exterior of the flexible polymer casing to an interior of the flexible polymer casing, and the infused electrode is coupled to the circuitry so as to allow the signal to pass from outside the flexible polymer casing to the circuitry. A polymer in a portion of the flexible polymer casing that is infused with the conductive material at the location is cross-linked with a polymer in a portion of the flexible polymer casing that is not infused with the conductive material.