The heating element 2 of FIG. 2 comprises a heat resistant support 2a, a coating 2b comprising heating material located on the support 2a, and a heat resistant protective coating 2c arranged so that the coating 2b comprising heating material is located between the support 2a and the heat resistant protective coating 2c. The heating material again is heatable by penetration with a varying magnetic field.

In this embodiment, the heating element 2 is substantially cylindrical with a substantially circular cross section, but in other embodiments the heating element 2 may have an oval or elliptical cross section. In some embodiments, the heating element 2 may have a polygonal, quadrilateral, rectangular, square, triangular, star-shaped, or irregular cross section, for example.

In this embodiment, the heating element 2 is elongate and has a longitudinal axis A-A. In other embodiments, the heating element 2 may not be elongate. In some such other embodiments, the heating element 2 still has an axial direction A-A that is perpendicular to the cross section of the heating element 2.

The heating element 2 has a hollow inner region 2i, and a wall thickness T that is measured between inside and outside diameters (or dimensions perpendicular to the axial direction A-A) ID, OD of the heating element 2. In some embodiments, the wall thickness T is no more than 1 millimeter, such as no more than 0.5 millimeters or no more than 0.3 millimeters. In some embodiments, the outside diameter or dimension OD is between 0.3 millimeters and 5 millimeters. In some embodiments, the inside diameter or dimension ID is between 0.1 millimeters and 2.1 millimeters.