What is the tube in the solar water heater tube?

Purple gold pipes are also highly prized by merchants. They make a few turns on the last layer of the three pipes. Colors appear as purple, red and other colors before blue. They are the same as other pipes when used on water heaters. It mainly consists of the bottom copper layer, the two middle absorption layers, which are usually a compound of the dielectric (aluminum nitride) and steel components, and the final anti-reflection layer, which usually uses aluminum nitride. and anti-reflective layers also use aluminum trioxide, but relatively rare