a. the pipe is made of super conductive oxygen-free copper. The general solar tubes transfer the heat energy by the water,but the super conductive pipe with the smallest surface ,can transfer the heat to a long distance by the copper pipe and the heat spoilage is almost zero ,possessing a very high heat conducting efficiency and a high speed.
b.No water inside, can protect from freezing or boiling ,more reliable and safe.
C.The evacuated tube  with the super conductive heat pipe is the most advanced technology in the world.
d.long service life and graceful appearabce keeps eco-friendly and be your best choice.