The carrier is the thickest, strongest part of the ribbon. With excellent thermal conductivity it ensures a uniform heat transfer to the ink and with good tear resistance (mechanical strength) to avoid rupture during operation.
The backcoating is that part of the ribbon which is the closest to the print head. Its function is to protect the print head (to avoid excessive heat and mechanical abrasion). For that, a low-quality backcoating can cause excessive friction between ribbon and print head and give premature wear to the print head.
The ink layer is that part of the ribbon that is actually transferred onto the packing paper. Depending on the application and the required print quality (detailing, sharpness), it can be made of resin, wax or a combination of both materials. Special additives or even a release layer can be added to achieve a better print when required.