What is the best material for the electric heating tube

The tubular electric heating element (electric heating tube) is made of a metal tube (including stainless steel and red copper tube), and spiral electric heating alloy wires (nickel-chromium, iron-chromium alloy) are uniformly distributed along the central axis of the tube. The gap filling pressure is Magnesium oxide sand with good insulation and thermal conductivity, both ends of the nozzle are sealed with silica gel. The metal armored electric heating element of the plate can heat the air, and the metal rights belong to the mold and various liquids.