Direct thermal or thermal transfer: which labels should you use?

Take an old petrol pump bill or ATM slip out of your wallet. Often the print has faded or the paper has turned grey. That slip is direct thermal paper, the same family of material as most courier labels.

Now picture the batch label on a paint drum that has stood in a yard for a year and still scans. A printed-on-demand label like that is usually thermal transfer.

Both methods use the same kind of printer and the same row of tiny heating dots. The difference is where the dark colour comes from.

That one difference decides how long your label lives.

My short answer is this. Use direct thermal for labels that live for days or weeks indoors and are then thrown away. Use thermal transfer for anything that must stay readable for months, sits in heat or sun, gets wet, oily or rubbed, or is printed on plastic film.

How direct thermal works

A direct thermal label carries a chemical coating that darkens with heat. The printhead heats tiny dots on that coating, and those dots turn black. There is no ink and no ribbon.

The weak point is simple. The coating is still active after printing. Zebra, the printer maker, calls direct thermal "extremely sensitive to environmental conditions such as heat and light" in its comparison of the two methods. Zebra also says it is not used for lifetime identification.

So a direct thermal label keeps reacting long after it leaves the printer.

A hot truck darkens the background. Sunlight and tube lights slowly fade the bars. Rubbing, water and oil can mark or smear the coating.

Some direct thermal papers carry a protective top coat that handles moisture and rubbing better. It helps. It does not make the label safe in heat or sun, so ask for the datasheet before you rely on it.

How thermal transfer works

A thermal transfer printer uses a ribbon, a thin film coated with ink. The printhead heats the back of the ribbon, and the ink melts onto the label at each heated dot.

The easiest picture I know is the old typewriter ribbon in a court office, only pressed by heat instead of a key.

The label needs no special coating. So the face can be paper, polypropylene (PP), polyester (PET) or other films.

How long the print lasts now depends on one thing we control: matching the ribbon to that face.

Ribbons: wax, wax-resin and resin

The guide to thermal transfer ribbons from Zebra sorts them into three grades.

What counts as a "harsh" chemical? The Zebra white paper Selecting the Right Label to Identify Your Finished Product (2023) gives a useful scale. Water and window cleaner are weak. Alcohol and bleach are moderate. Oil and petrol are harsh. Acetone and xylene are extreme.

Two practical rules come with ribbons, and I would print both on the wall next to the printer.

1. Use a ribbon at least as wide as the label. The Zebra ZT510 ribbon specifications ask for this to protect the printhead from wear.
2. Match the ink side to the printer. Ribbons are wound with the ink on the outside or the inside, and many printers take only one. The Zebra ribbon test with adhesive takes 10 seconds. Press the sticky side of a label onto the outside of the ribbon roll and peel it off. If ink comes away on the label, the ink is on the outside.

How long does each one last?

The same white paper gives a pair of examples I find useful. A label that must stay readable for 6 months, with no chemicals, moisture or rubbing, is a direct thermal paper job. A label on an item stored outdoors for more than 3 years, in contact with moderate chemicals, needs a thermal transfer synthetic label.

Every label you print falls somewhere between those two.

GS1, the barcode standards body, goes further for pallet and carton labels. Its Logistic Label Guideline (Release 1.3, July 2019) says material or ink sensitive to heat is not acceptable, and names thermal paper that changes colour in heat or sun as the example to avoid.

Then why are courier labels direct thermal? Because a courier label lives for a few days and is thrown away with the box. A pallet label for a retailer's warehouse can sit on a rack for months.

In my view, that difference in life should decide the method, not the printer you already own.

Indian conditions push the line further. A godown with a tin roof in May, a truck parked in the sun on the highway, a monsoon-damp store room: each one shortens the life of a direct thermal print.

When in doubt, I would choose thermal transfer.

What drives the cost

I will not quote prices here, because they change. These are the 5 things that move the cost per label up or down.

1. Consumables. Direct thermal uses only the label. Thermal transfer uses a label and a ribbon, so Zebra notes that its supply cost is higher.
2. Printhead life. Zebra also says thermal transfer printheads last longer than direct thermal ones. The head is a costly spare, so this offsets part of the ribbon cost.
3. Ribbon waste. The ribbon runs as wide as you load it. A narrow label on a wide ribbon wastes ink film on every print, so match the ribbon width to the label width, but never go narrower.
4. Speed. The white paper says synthetic labels usually do not give quality barcodes above 6 inches per second. Printing at 12 inches per second or more needs thermal transfer paper with a high-speed wax ribbon.
5. Failure. A label that fades in the warehouse costs relabelling, a rejected delivery, or a stock count that never matches.

Here is the rule of the trade I would go by. The cheapest label is the one that still scans on the last day it is needed.

The price per thousand comes second.

A decision table

Common mistakes

1. Using direct thermal labels on products with a long shelf life, because the printer was already there.
2. Using a wax ribbon on PP or PET. It may look perfect on day one and smear later.
3. Loading a ribbon narrower than the label, which wears the printhead where the ribbon does not cover it.
4. Turning darkness up to fix a faint print before checking whether the ribbon suits the label. Zebra's ZT211 guide shows that too much darkness makes bars grow and fills in small text, which can lower the scan grade.
5. Storing direct thermal rolls in a hot godown or near a window before they are even printed.
6. Skipping printhead cleaning. Zebra's ZT111 cleaning schedule asks for it after every roll of labels in direct thermal mode and every roll of ribbon in thermal transfer mode, with 99.7% isopropyl alcohol. The manual for your own model may differ, so follow it.

Test before you decide

A table can only guide you. I cannot tell you how long your label will last from here, and neither can any supplier. Your own pack, in your own godown, will tell you in a week.

1. Print the same barcode by both methods, on the face stock you plan to use.
2. Stick both on the real pack.
3. Keep one pair on a sunny window ledge, one pair in the hottest corner of your store, and one pair where the pack normally lives.
4. Rub each one with a cotton bud dipped in whatever it will meet in real life: water, hand sanitiser, cooking oil or diesel.
5. Scan every label at the start and again after 7 days. Note which ones read on the first try.

Labels are made by Jagannath Labels, our group's label company. Still, we would rather you run this test than take our word for it. If you want a second opinion on the results, send us the photos and your printer model through the contact page. If adhesion is your problem rather than print, our lesson on label adhesives covers that side.