Thermal Paper is special fine paper that is coated with a chemical that changes color when exposed to heat. Thermal paper is used in Point-of-Sale (POS) printers such as credit card terminals, cash registers, adding machines and similar devices because it does not require a POS ink ribbon or cartridge to display information

Thermal Paper is special type of paper that, when in contact with heat, changes its

colour to black or, sometimes, to blue or red. The terms " heat-sensitive paper' and 'audit roll' are often used as synonyms for thermal paper.

Thermal Paper is a special fine paper that is coated with a material formulated to change color locally when exposed to heat. It is used in thermal printers, particularly in inexpensive devices such as adding machine, cash registers and credit card terminals and small, lightweight portable printers.

The surface of the paper is coated with a substance which changes color when heated above a certain temperature. The printer essentially consists of a transport mechanism which drags the paper across a thermal dot matrix print head. The (very small) dots of the head heat up very quickly to imprint a dot, then cool equally quickly.

Most thermal papers' coatings turn black when heated, but coatings that turn blue or red, and multicolor coatings, are sometimes used. An unintended heat source, such as a coffee cup, can discolour the paper and obscure any printing. A fingernail rubbed quickly across the paper may generate enough heat from friction to produce a mark.

The thermal paper starts as base paper made of wood pulp. The paper is then primed with a chemical known as the precoat. The precoat fills any pores or spaces between the fibers of the paper. The precoat assures that the printing surface is smooth and even.

This chemical also absorbs and stabilizes the dyes once they are activated. The precoat also keeps the print head free from accumulating melted dye.

The chemical mixture that is applied as a topcoat is called the thermal coat. This coat is a mixture of chemicals that change colors when exposed to heat.

The thermal layer contains leuco dyes, sensitizers, and developers. The leuco dye contains clear crystals that turn black once the heat from the printer heads touch the paper.

The thermal mixture also contains either Bisphenol-A (BPA) or Bisphenol-B (BPS). These chemicals act as developers. Sensitizers are added to the thermal mix to adjust the image activation temperature of the coating.