A heat-fusible gasket for affecting a flexible seal between two adjoining components of a coupling, such as the spigot end of a section of plastic pipe and a bell coupler to be fitted thereover. The gasket has an inner core which is constructed of an elastomeric material, and outer opposing sealing surfaces that are formed at least in part of a heat-fusible material that is compatible with the heat-fusible components with which the gasket is intended to engage. The gasket is co-extruded in continuous lengths with electrically conductive heat resistance wires embedded in the outer compatibly heat-fusible layers. For annular gaskets, the co-extruded lengths of gasket material may be cut and spliced into any desired diameter gasket. Upon connection to a power source, the gasket seal is perfected through electrofusion along the opposing sealing surfaces of the gasket, thereby providing enhanced sealing capability.