Direct thermal and thermal-transfer printing both use a heated print-head to print on blank labels. However, with direct thermal printers, the print-head must be in direct contact with the label material, while thermal-transfer printers use an ink ribbon to print, made of wax or resin, and this is what comes into contact with the heated print-head.
As such, direct thermal applies heat directly to the label, which reacts with the label’s coating to generate a printout, whereas thermal-transfer printers apply heat to the ribbon, allowing the ink to then be transferred to the label.