Two kinds of thermal label, and why the difference matters
Almost every shipping label, warehouse location tag, retail price label and product barcode you see is printed by a thermal printer. These printers are cheap to run, fast and reliable, which is why they sit on packing benches everywhere. But there are two quite different technologies hiding under the word "thermal", and choosing the wrong one is the usual reason barcodes stop scanning after a few weeks.
Direct thermal printing uses heat-sensitive label stock that darkens where the print head heats it. Thermal transfer printing uses a ribbon, and the print head melts ink from the ribbon onto the label. This guide explains how each works, which labels suit which job, how pre-printed thermal labels are made and how to keep barcodes readable.
Direct thermal labels
Direct thermal labels have a chemical coating that turns black when heated. There is no ink or ribbon. The printer simply heats tiny points on the head to create text and barcodes.
Where direct thermal works well
- Shipping and courier labels that only need to last until delivery.
- Receipts, queue tickets and short-life price labels.
- Food labels for products with short shelf life, kept away from heat.
Its limits
The coating keeps reacting after printing. Heat, direct sunlight, some plastics, oils and friction can darken the whole label or fade the print. Over months, even in normal conditions, contrast drops. A direct thermal barcode that scanned perfectly on day one may fail in storage. Top-coated direct thermal stock resists moisture and scuffing better than uncoated stock, but it is still not a long-life label.
Thermal transfer labels
Thermal transfer printers use a ribbon coated with ink. The heated print head melts the ink onto the label surface, where it bonds as it cools. The label itself is not heat-sensitive, so it does not darken or fade from heat in the same way.
Choosing the ribbon
- Wax ribbons suit paper labels for general use: cartons, shelf labels and indoor product labels.
- Wax-resin ribbons give better scratch and smudge resistance on paper and some synthetic labels.
- Resin ribbons are the most durable, used on synthetic films such as polypropylene and polyester for labels that face chemicals, heat, outdoor exposure or repeated handling.
The ribbon and the label face must be matched. A resin ribbon on an uncoated paper label is wasted, and a wax ribbon on a polyester label can rub off. Label suppliers publish compatibility notes; follow them. For a wider view of facestocks and adhesives, see our guide to choosing durable label materials.
Pre-printed thermal labels: logos plus variable data
Many businesses want a branded label with a logo, colour panel and fixed text, plus variable information such as an address, batch number or barcode added at the packing bench. The usual approach is a two-step process:
- The label is printed in full colour on a roll, using digital or flexographic label printing, with blank areas left for variable data.
- The variable data is added later on a thermal printer in the warehouse or shop.
For this to work, the pre-printed areas must be compatible with the thermal printing that follows. Direct thermal stock can be pre-printed, but heavy ink or varnish over the thermal coating can stop it reacting, so leave the variable area completely clear. For thermal transfer, the pre-printed inks and any varnish must accept the ribbon; your printer should test this before a large run. Core size, label gap, wind direction and outside diameter also need to match your desktop or industrial printer. Our article on roll labels and unwind direction covers those specifications.
Keeping barcodes readable
A thermal label usually exists to carry a barcode, and a barcode that does not scan is worse than useless at a busy loading bay or till. A few habits make a large difference:
- Use enough resolution. Many desktop thermal printers print at 203 dpi, which is fine for standard shipping barcodes. Small barcodes and 2D codes on tiny labels often need 300 dpi or more.
- Respect the quiet zone. Leave clear space on both sides of a linear barcode. Placing it up against the label edge or a printed border causes scan failures.
- Mind the print direction. Barcodes printed with bars running in the same direction as the label moves through the printer (often called picket fence orientation) tend to print with cleaner edges than bars running across the head.
- Do not shrink below the standard. Retail and logistics barcodes have minimum sizes set by the relevant standards. Scaling one down to fit a design is a common error.
- Keep heads clean and settings right. Dirty print heads leave white lines through bars, and too much heat causes bars to spread. Many scan problems are maintenance problems.
For barcodes and serial numbers that are printed on the press rather than at the bench, our guide to variable data printing explains how they are generated and checked.
Storing thermal labels before use
Label stock has a shelf life of its own, and the way rolls are stored affects how they print. Direct thermal rolls are the most sensitive: keep them in their packaging, away from windows, radiators and warm delivery vans, because heat and light can start to discolour the coating before a single label is printed. Thermal transfer ribbons and labels are more forgiving, but very humid or dusty storage still causes problems, from labels that will not peel cleanly to dust on the print head.
Order in quantities you will use within a reasonable period rather than a year's supply at once, and rotate stock so older rolls are used first. If you notice greyish backgrounds on new direct thermal labels or faint, patchy print on thermal transfer stock, check the storage conditions and the batch before blaming the printer.
Testing before a large order
Before switching to a new label, ask for a sample roll and run it on your own printer with your normal settings. Print a batch, scan the barcodes, rub a few with a thumb, leave some on a sunny shelf for a week and see how they look. It is a simple test and it tells you more than any specification sheet.
Which thermal label should you choose?
| Use | Usually the better choice |
|---|---|
| Courier and shipping labels | Direct thermal, top-coated if parcels may get wet |
| Warehouse location and shelf labels | Thermal transfer on paper or synthetic, wax-resin ribbon |
| Product labels kept for months or years | Thermal transfer, often on synthetic film with resin ribbon |
| Chilled or frozen food | Stock and adhesive rated for cold, matched to the printing method |
| Outdoor, chemical or high-heat use | Thermal transfer with resin ribbon on polyester or similar film |
If you are unsure, the question to answer is simple: how long must this label stay readable, and what will it touch along the way?
Thermal label printing at Disc-Print
We supply plain and pre-printed thermal labels on rolls for direct thermal and thermal transfer printers, in paper and synthetic facestocks, with core sizes and wind directions to match your machines. For branded labels we print your logo and fixed artwork in full colour and leave clean areas for your own variable data, and we test samples on the type of printer you use before running the full quantity.
Tell us your printer model, label size, quantity and how long the labels need to last, and we will recommend a stock and ribbon combination. Read more about print materials and quality or contact us for samples and a quote.
