Disclosure is made of a novel sheath and the method of its use for protecting electrical conductors and connections. The sheath comprises a tubular body which defines an interior space. The space contains an expandable, synthetic, polymeric resin foam forming composition. The method of the invention comprises inserting an electrical conductor or connection into the sheath of the invention and activating the foam forming composition to foam and encapsulate the conductor or connection. The installed sheaths protect the conductors and/or connections from degradation by environmental conditions, are resilient and improve the insulative quality of the electrical connection.