Thermal print heads can have a resolution of up to 1,200 dots per inch (dpi). The heat generated activates the paper's thermochromic layer, causing it to turn a certain color (for example, black). The printer sends an electric current to the heating elements of the thermal head. In order to print, the thermal paper is inserted between the thermal head and the platen and pressed against the head. This process is usually monochrome, but some two-color designs exist, which can print both black and an additional color (often red) by applying heat at two different temperatures. When the matrix is heated above its melting point, the dye reacts with the acid, shifts to its colored form, and the changed form is then conserved in metastable state when the matrix solidifies back quickly enough, a process known as thermochromism. Thermal paper is impregnated with a solid-state mixture of a dye and a suitable matrix, for example, a fluoran leuco dye and an octadecylphosphonic acid. Р”Р„ thermal printer typically contains at least these components: Thermal transfer printing is a different method, using plain paper with a heat-sensitive ribbon instead of heat-sensitive paper, but using similar print heads.

Most thermal printers are monochrome (black and white) although some two-color designs exist. The coating turns black in the areas where it is heated, producing an image. Thermal printing (or direct thermal printing) is a digital printing process which produces a printed image by passing paper with a thermochromic coating, commonly known as thermal paper, over a print head consisting of tiny electrically heated elements.

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