Portable printers work in one of three ways. Thermal transfer printers work much like a typewriter, using heat and pressure to transfer images from a ribbon to the page. Ink-jet printers use small cartridges of liquid ink, spraying very fine drops through a nozzle to create images.

Thermal printers operate like older fax machines These models use heat-sensitive, which is marked with a small heating device.

The main advantage of thermal and thermal transfer printers is that they can be very small. The smallest thermal printer weighs only 14 ounces, while the smallest thermal transfer printer weighs only 1.1 pounds. In contrast, ink-jet printers start at about 2.4 pounds.

On the other hand, ink-jets generally produce much better output than thermal transfer and thermal models. Ink-jets can produce decent images, particularly if very smooth paper is used. Thermal transfer machines often leave large horizontal bands on dark areas, while thermal printers require a special type of paper.