Direct thermal or thermal transfer: how long the print must survive, and how much friction it takes. Plus the failure signals of each.
Both technologies print without wet ink, and both feed the same thermal printers. The difference is where the image comes from: direct thermal paper darkens where the print head heats it directly; thermal transfer melts a ribbon onto the face stock. That single difference decides price, durability and shelf life.Days to weeks (express waybills, picking labels, fresh-food dates): direct thermal, which is cheaper and ribbon-free. Months to years (asset tags, serial plates, long-shelf-life goods): thermal transfer, whose image does not keep developing after printing. Signal that direct thermal was wrong: variable grey haze across the whole label after storage.
Waybills run through sorters and against other parcels; freezer stock is handled with gloves. Direct thermal surfaces scratch; thermal-transfer images sit under a tougher face. Signal: barcode edges eroding after a single conveyor line.
A ribbon, a printer fitted for ribbon, and slightly slower line speed. In exchange, the same face stock prints with far higher durability, and you can choose wax, wax-resin or resin ribbons to match the surface. For a catalogue of both classes, see thermal paper and thermal transfer paper.
Rule of thumb: if the label's job ends when the parcel is delivered, direct thermal is usually right. If the label has to stay readable longer than the parcel exists, print thermal transfer.
Direct thermal paper darkens through a heat-sensitive coating, and that coating keeps reacting: heat, sunlight, abrasion and even plasticizer contact continue to develop the surface. Prints meant to survive months should use thermal transfer instead.
Lamination adds heat and pressure at application, which can pre-darken thermal paper. If protection is needed, thermal transfer on a tougher face stock is the cleaner route.