Abstract: A foil element for the electric heating of objects comprises a resistance heating coil placed between insulating plastic foils and a sensor coil placed between the plastic foils beside the heating coil. The sensor and heating coils are formed of the same metallic material. The sensor coil is spaced sufficiently far from the heating coil to assure that the sensor coil is heated mainly by heat flowing to or from the object being heated and only slightly by heat directly from the heating coil. The electric resistance of the sensor coil is sensed to determine the temperature thereof. The heating coil is controlled in accordance with the temperature of the sensor coil.

Abstract: Method of manufacturing two loop-formed metal foil elements (1,2) intended to serve as electrical resistance heating elements. Starting from a unitary metal foil, possibly enclosed by plastic foils, at least two complementarily extending loop elements, one inside the other.

Abstract: A resilient snap-on electric heating jacket for heating tubular objects includes a thin sheet of flexible plastic material constituting a radially internal curved surface adapted to engage the surface of the object. A pattern of spaced electrically conductive loops are formed on the radially external surface of the sheet to define an electric heating element. A thick resilient support member of polymeric material coextensive with and overlying the external surface of the plastic sheet and the foil loops is directly secured to the external surface portions of the foil loops and the plastic sheet by an autogenous bond to form a unitary structure generally C-shaped in cross section and capable of being snapped onto a tubular object the outer diameter of which corresponds approximately to the inner diameter of the profile of the unitary structure. The profile of the support member encloses an angle between 180.degree. and 270.degree. and preferably between 200.degree. and 250.degree..