What Are Thermal Labels and How Do They Work?

If you've ever received a parcel with a shipping label on it, there's a very good chance it was printed on a thermal label. They're the standard for courier and postal labels across the UK, used by Royal Mail, Evri, DPD, Hermes and most other delivery services. Yet for a lot of people getting started with selling online or setting up a small dispatch operation, thermal labels are something they know they need without fully understanding what makes them different from ordinary sticky labels.

This guide covers what thermal labels are, how they work, the difference between direct thermal and thermal transfer printing, and how to know which type you need.

What are thermal labels?

Thermal labels are self-adhesive labels printed using heat rather than ink. Instead of a printhead spraying or pressing ink onto the label surface, a thermal printer uses a row of tiny heating elements to activate a heat-sensitive coating on the label, which darkens on contact with heat to form text, barcodes and graphics.

The result is a printed label with no ink cartridges, no toner, and no ribbon required for the most common type used in shipping. This makes thermal printing fast, low-maintenance and cheap to run once you have the hardware, which is why it's the dominant method for producing shipping labels at any meaningful volume.

How do thermal labels work?

The label material itself does the work. A direct thermal label has a coating applied to its surface that contains a heat-reactive compound, typically a mixture of a leuco dye and a developer chemical. At room temperature these two components are physically separated and the coating appears white. When heat is applied above a certain threshold, the dye and developer react together and produce a dark colour, typically black, wherever the heating element made contact.

The thermal printer controls which heating elements activate and when, forming characters and barcodes by selectively darkening specific areas of the label as it passes through the printhead. The process takes a fraction of a second per label and produces a crisp, high-resolution print without any consumables beyond the label roll itself.

Labels are fed through the printer either on a continuous roll, where the printer cuts or the user tears between labels, or pre-cut and stacked in fanfold format, where the labels are folded into a concertina stack and fed from a box rather than a roll. Both formats print the same way.

Direct thermal vs thermal transfer: what is the difference?

There are two distinct thermal printing methods. Understanding the difference matters because they use different labels and different printers, and mixing them up means unusable labels.

Direct thermal printing

Direct thermal printing works exactly as described above. The printhead heats the label surface directly, activating the coating on the label to produce the printed image. No ribbon or ink is involved. The printer needs only the label roll to operate.

Direct thermal is the standard method for shipping labels. It's fast, cost-effective and produces consistent barcode quality for scanning at courier sortation points. The labels from a direct thermal printer will fade over time when exposed to prolonged heat or direct sunlight, but for shipping labels that travel through a courier network and are scanned within days or weeks of printing, this is not a practical concern.

If you're printing Royal Mail, Evri, DPD or similar courier labels from a platform like Royal Mail Click and Drop, Vinted, eBay or Shopify, direct thermal is what you need. The label printers most commonly used for this, including Zebra, Rollo, Munbyn and similar models, are direct thermal printers.

Thermal transfer printing

Thermal transfer printing uses the same heat-based printhead mechanism, but instead of activating a coating on the label surface, the heat melts ink from a separate ribbon onto the label. The ribbon, which is a thin film coated with wax or resin-based ink, sits between the printhead and the label. Heat transfers the ink from the ribbon to the label surface, where it bonds permanently.

The advantage of thermal transfer is durability. Labels printed this way are resistant to heat, moisture, chemicals and UV light, which makes them suitable for applications where the label needs to last for months or years: product labels on goods stored outdoors, laboratory samples, chemical containers, asset tags and similar. The image does not fade in the way a direct thermal print can.

The tradeoff is ongoing cost. Thermal transfer requires a ribbon consumable in addition to the label roll. Ribbons need replacing periodically, which adds to the per-label cost compared to direct thermal.

For shipping labels and most e-commerce applications, thermal transfer is unnecessary. Direct thermal does the job at lower ongoing cost. Thermal transfer is the right choice when label longevity under harsh conditions is a requirement.

How do you tell direct thermal and thermal transfer labels apart?

The easiest way is to scratch the label surface with a fingernail. A direct thermal label will leave a dark mark where the friction generates enough heat to activate the coating. A thermal transfer label will not react this way because the surface is not heat-sensitive. It requires ink from a ribbon to produce a mark.

You can also check the label packaging or product listing. Direct thermal labels are almost always described as such. If a label is listed without specifying the print method, it's likely direct thermal, as this is the far more common format for general shipping use.

What size thermal labels do you need?

The most widely used size for UK courier and shipping labels is 4x6 inches, also written as 6x4 inches or 100x150mm. This is the format used by Royal Mail Click and Drop, Evri, DPD, Hermes, Amazon and most other UK courier platforms. If you're printing shipping labels from any of these services, 4x6 is the size you need.

Our white thermal labels in 4x6 inch are the standard choice for this. They're compatible with all direct thermal label printers and work with every major UK courier platform.

For smaller labels used for product tagging, returns labels, or address labels that don't need the full 4x6 format, our white thermal labels in 4x4 inch are a practical alternative.

Roll labels vs fanfold labels

Thermal labels come in two physical formats and both print identically. The choice between them is about how your printer feeds labels and how much space you have on your packing bench.

Roll labels are wound on a core and fed from the back or top of the printer as the roll unwinds. They're the most common format and work with all standard direct thermal label printers. The roll sits inside or behind the printer and feeds continuously until it runs out.

Fanfold labels are cut and stacked in a concertina fold, packed in a box. They feed from a stack rather than a roll, which means you can store a very large quantity of labels in a compact box and feed them continuously without changing rolls. This is particularly useful for high-volume operations where stopping to change a label roll interrupts packing flow. The printer feeds from the stack the same way it feeds from a roll.

Our white fanfold thermal labels in 4x6 inch are a good choice for anyone dispatching a significant volume of orders daily, or anyone who wants to keep a large label stock on hand without multiple rolls taking up bench space.

What about coloured thermal labels?

Most shipping labels are white, but coloured thermal labels have practical uses in warehouse and dispatch environments. Colour-coded labels can be used to identify orders by priority, destination, product category, or return status at a glance, which speeds up sorting and picking without needing to read the label detail on every one.

Our blue thermal labels in 4x6 inch are a direct thermal label in the standard shipping format and print exactly the same as white labels. They're popular with businesses that want to visually distinguish between different order types or fulfilment lanes without changing their labelling workflow.

Do thermal labels work with any printer?

Direct thermal labels require a direct thermal printer. They will not print correctly in a standard inkjet or laser printer because those machines do not use a thermal printhead. Running a thermal label through an inkjet printer may damage the printhead or produce no usable output.

The most widely used direct thermal label printers for UK e-commerce and marketplace sellers include the Zebra ZD series, Rollo, Munbyn, Phomemo and several others. All of these use the same label format and are compatible with the 4x6 labels in the Mr Bags range.

Before buying labels, check your printer's specification for the label size and core diameter it accepts. Most standard printers take labels on a 76mm (3 inch) core. Some compact models use a 25mm or 38mm core. The label format and print quality are the same regardless of core size.

Why use thermal labels rather than printing on paper?

There are a few reasons thermal labels have become the standard for shipping rather than printing labels on plain paper and taping them to a box.

Thermal labels have a permanent self-adhesive backing rated for courier handling. They bond to the box surface and stay bonded through the mechanical stress of sorting systems, varying temperatures, and moisture in transit. A paper label taped to a box can peel, tear or become unreadable if the tape gets wet.

Barcode quality is consistently high on thermal labels. Courier scanning systems rely on clean barcodes to route parcels automatically. A barcode printed on a thermal label and scanned within normal courier conditions will read reliably. A barcode printed on a home inkjet printer on plain paper and covered with tape is more likely to fail a scan, causing manual handling and delays.

Thermal printing is also faster and cheaper per label at volume. No ink cartridges, no waiting for prints to dry, no smearing. A thermal label printer produces a label in under two seconds with no ongoing consumable cost beyond the label roll.

You can browse the full range of thermal labels, including 4x6 roll and fanfold formats, 4x4 labels and coloured options, on our thermal labels page.