The flexible tubular heater GC-flex D-shape or GC-flex square are delivered ex-stock in various sizes and can be bent to fit virtually any 2D or 3D groove using the GC-flex tool set, for example. The outer sheath, made of woven pure nickel, adapts to any curvature and presses itself evenly against the surface of the groove. This guarantees optimal heat transfer even when under extreme mechanical stress.