The upper roller manufacturer tells you that the upper fixing roller is located at the upper part of the fixing device, and the high temperature required for fixing is conducted by this part and applied to the toner image on the copy paper. It is an aluminum hollow tube, and its outer layer is coated with a chemical coating film that is resistant to high temperature (generally around 180 degrees).

The manufacturer of the upper roller tells you that the hollow part is used to install the fixing lamp that generates high temperature. The coating part is generally black, but also has other colors, shiny, and the two ends are relatively thin. It is used to fix and install the driving gear.
The manufacturer of the upper roller tells you that the middle of the lower fixing roller is a solid steel roller. Most of the middle (corresponding to the upper fixing roller) is covered with a rubber layer with a thickness of about 0.8CM, which is generally red and covered with a thin layer on the rubber layer. High temperature resistant (about 80 degrees) chemical film.
The upper roller manufacturer tells you that its main function is to put pressure on the fixing upper roller, and it has no drive itself. The power of its rotation comes from the friction of the upper fixing roller, and the rotation of it and the upper fixing roller can fix the copy toner image through high temperature and send it to the output tray of the copier.