Heating elements are made by inserting electrical heating wires into seamless metal tubes (carbon steel, titanium, stainless steel, copper) and then filling the voids with magnesium oxide powder, which has excellent thermal conductivity and insulation properties, before shrinking the tube. They are then processed into various shapes as required by the customer. They feature a simple structure, high thermal efficiency, good mechanical strength, and excellent adaptability to harsh environments. They can be used for heating various liquids and acidic, alkaline, and saline solutions, as well as for melting metals with low melting points (e.g., lead, zinc, tin, bismuth alloys).