Thermal printing has its own small vocabulary, and most of it gets thrown around without explanation on printer spec sheets and courier setup pages. If you've just bought your first thermal printer, here's what the terms actually mean.
Direct thermal
A printing method that uses heat-sensitive paper. The printhead applies heat directly to the label in the shape of the text and barcode, and the coating darkens on contact — no ink, toner or ribbon required. Nearly all UK shipping labels are printed this way. See our full direct thermal vs thermal transfer comparison for more detail.
Thermal transfer
A related method that melts ink from a ribbon onto plain label stock using the same heated printhead. It produces prints that resist fading over years rather than days, which matters for asset tags and product labelling but is unnecessary for a courier label that's scanned once or twice.
Core size
The diameter of the cardboard tube a label roll is wound around. Most desktop thermal printers take a 25mm core; order the wrong one and the roll simply won't sit on the spindle. Our core size guide covers how to check yours.
DPI (print resolution)
Dots per inch — how finely the printhead can render text and barcodes. 203 DPI is the standard for shipping labels and is more than sharp enough for any courier barcode; higher DPI (300+) matters more for small, dense barcodes on product packaging than for a 4×6 shipping label.
Print darkness / heat setting
A driver-level setting controlling how much heat the printhead applies. Too low and the print comes out faded or patchy; too high and it can shorten printhead life and cause labels to curl. Different label stocks respond slightly differently, which is why switching brands of roll sometimes means re-tuning this setting.
Gap sensor / black mark sensor
The sensor that tells the printer where one label ends and the next begins, so it feeds and cuts (or tears) at the right point. A dirty or miscalibrated sensor is a common cause of labels printing across the gap between two labels rather than centred on one.
Label liner
The backing paper a label peels away from. It's waste by design, but it's worth knowing it's there when troubleshooting jams — a liner that's not feeding smoothly through the printer is a common, easily fixed cause of paper jams, covered in our guide to choosing a thermal label printer.
Skip the jargon — just buy labels that work
Our 4×6 direct thermal rolls are pre-specified for every major thermal printer, so you don't need to decode a spec sheet to get started.
Shop 4×6 Labels