An ink cartridge, more commonly known as an inkjet cartridge, is the replaceable component of an inkjet printer. It contains ink, and sometimes a print head, that is spread on paper during printing.

The majority of ink cartridges contain one or more partitioned ink chambers. Ink cartridges with one chamber often contain black ink, but in the case of manufacturers like Epson and Canon they may contain cyan, magenta, or yellow ink. Single chamber, individual color, cartridges have become popular over the last few years. Multi-chamber ink cartridges contain a chamber each for cyan, magenta, and yellow ink. Manufacturers like HP, Lexmark, and Dell favor this multi-chamber cartridge approach over the individual chamber.

There are two types of ink cartridge design, thermal and Piezo.

Thermal – Most home and office inkjet printers use a thermal inkjet technology. Inside each partition of the cartridge is a heating element with a tiny metal plate or resistor. In response to a signal given by the printer, a tiny current flows through the metal or resistor making it warm, and the ink immediately surrounding the heated plate is vaporized into a tiny air bubble inside the nozzle. As a consequence, the total volume of the ink exceeds that of the nozzle. An ink droplet is forced out of the cartridge nozzle onto the paper. This process takes a matter of milliseconds.

Printing depends on the smooth flow of ink, which can be hindered if the ink begins to dry at the print head, as can happen when an ink level becomes low; dried ink can be cleaned from a cartridge print head, by gentle rubbing with isopropyl alcohol on a swab or folded paper towel.

The ink also acts as a coolant to protect the metal-plate heating elements: when the ink supply is depleted, and printing is attempted, the heating elements in thermal cartridges often burn out, permanently damaging the print head. When the ink first begins to run thin, the cartridge should be refilled or replaced, to avoid over-heating damage to the print-head.

Piezoelectric – All Epson printers use a piezoelectric crystal in each nozzle instead of a heating element. When current is applied, the crystal changes shape or size, forcing a droplet of ink from the nozzle. This allows use of inks which react badly when heated, and can produce a smaller ink drop in some situations than thermal inkjet schemes.