How Does an Inkjet Printer Work? Thermal vs. Piezo Printheads Explained

Quick answer: an inkjet printer builds a page from millions of microscopic ink droplets. A printhead with hundreds or thousands of tiny nozzles slides back and forth across the paper on a carriage, firing droplets only a few picoliters in size exactly where the image needs them, while rollers advance the paper a fraction of an inch after every pass. The droplets are fired in one of two ways: thermal inkjet (HP, Canon) heats the ink to form a bubble that pushes a drop out, and piezo inkjet (Epson, Brother) flexes a crystal to squeeze a drop out without heat.

Updated October 8, 2026 · By William Elward, founder of Castle Ink (helping people with printers and ink since 2005)

What Is an Inkjet Printer?

An inkjet printer is a printer that sprays liquid ink directly onto paper, as opposed to a laser printer, which fuses dry toner powder onto the page. Inkjets are the most common type of home printer because they're inexpensive to buy, print excellent color photos and handle many kinds of paper. They range from $60 all-in-ones to ink-tank models like Epson EcoTank and Canon MegaTank, and up to wide-format printers used for posters and signs.

What Are the Main Parts of an Inkjet Printer?

• Printhead: a chip with rows of microscopic nozzles that fire the ink. It's either built into each cartridge or a permanent part of the printer.
• Ink cartridges or tanks: hold the ink (usually cyan, magenta, yellow and black) and feed it to the printhead.
• Carriage and belt: carry the printhead side to side across the page, driven by a motor.
• Encoder strip: a clear plastic strip printed with fine lines that tells the printer exactly where the printhead is, so dots land in the right place.
• Paper feed rollers and stepper motor: pull the sheet in and advance it precisely after each pass.
• Service station: the "parking spot" at one end where the printhead is capped, wiped and primed to keep nozzles from drying out.
• Controller board: turns your document into dot patterns and timing signals for every nozzle.

How Does a Thermal Inkjet Printhead Work?

Each nozzle sits over a tiny chamber with a thin-film resistor (a heater). When the printer wants a dot, it sends a pulse of current lasting only a few millionths of a second. The heater flash-boils a thin layer of ink into a vapor bubble, the expanding bubble pushes a droplet out of the nozzle, and as the bubble collapses it draws fresh ink in from the cartridge. The cycle repeats thousands of times per second per nozzle. Canon and HP developed the technology independently in the late 1970s; Canon still calls it "Bubble Jet" (see Wikipedia's history of inkjet printing).

Because heaters wear out, many thermal printers put the printhead on the cartridge itself, so you get a fresh printhead every time you change ink. That's the design in cartridges like the HP 61XL black and HP 61XL tri-color: the copper contacts and nozzle plate on the bottom are the printhead.

How Does a Piezo Inkjet Printhead Work?

Piezo printheads replace the heater with a piezoelectric element, a ceramic crystal that changes shape when voltage is applied. A pulse makes the crystal flex, which squeezes the ink chamber and forces a droplet out; relaxing it draws ink back in. There's no heat, so piezo heads can use a wider range of inks (including sublimation and other specialty inks), and by changing the voltage waveform they can fire several droplet sizes from the same nozzle. Epson says its Micro Piezo heads produce up to five droplet sizes and fire tens of thousands of times per second per nozzle (Epson Micro Piezo technology).

Piezo printheads cost more to make, so Epson and Brother build them into the printer as a permanent part. The cartridges, like the Epson 252XL 4-pack, are simple ink containers with a chip. The trade-off: if a permanent head clogs badly, you have to clean it rather than replacing a cartridge.

Thermal vs. Piezo: Which Is Better?

Neither is simply "better." Both produce excellent prints. Thermal designs make a clogged head easy to fix; piezo designs make cartridges cheaper and enable specialty uses like converting an EcoTank to sublimation.

How Does an Inkjet Printer Make Different Colors?

It mixes four process colors (cyan, magenta, yellow and black) as patterns of tiny dots. Your eye blends dots that are too small to see individually into a continuous color. Lighter shades use fewer, more widely spaced dots; deeper colors overlap more ink. Photo printers add light cyan, light magenta, gray or red inks for smoother gradients. The printer's resolution, quoted in dots per inch, determines how finely those dots can be placed. See inkjet printer resolution (DPI) explained; for what the ink itself is made of, see what printer ink is made of and pigment vs dye ink.

Why Does My Inkjet Printer Use Ink When I'm Not Printing?

To keep thousands of microscopic nozzles from drying out, the printer periodically primes and cleans the printhead at the service station, especially when it's powered on after a long rest or when you replace a cartridge. That flushes a small amount of ink into a waste-ink pad. It's also why turning the printer off at a power strip (instead of with its own button) is a bad idea: the head may not get capped properly. Printing at least one page a week keeps nozzles healthy.

What Goes Wrong With Inkjet Printers?

• Clogged nozzles cause streaks, missing lines and wrong colors. Start with printer missing lines and when a printhead cleaning kit beats the built-in cycle.
• Blank pages usually mean an empty, dried-out or air-locked cartridge, or tape left on a new one.
• Smearing happens when ink doesn't dry fast enough, often due to the wrong paper setting.
• Cartridge errors are usually dirty contacts or chip issues. See how to fix printer ink cartridge issues.

For everything else, browse the printer troubleshooting center.

Should I Buy an Inkjet or a Laser Printer?

Choose inkjet if you print photos, color projects or crafts, or print in small bursts. Choose laser if you mostly print black-and-white text in volume. Toner doesn't dry out, and cost per page is lower. Our full comparison is inkjet vs laser printer, and the 60-second PrinterIQ Finder quiz can match you with a printer.

Frequently Asked Questions

How small is an inkjet ink droplet?

Just a few picoliters, which is a few trillionths of a liter. The smallest drops on photo printers are around 1–2 picoliters, far smaller than a speck of dust.

Does an inkjet printer heat the paper?

No. Thermal inkjets heat only a microscopic layer of ink inside the nozzle for a few millionths of a second; the paper stays at room temperature. Laser printers are the ones that heat the page.

Who invented the inkjet printer?

Continuous-flow inkjet dates to the 1950s, but the drop-on-demand thermal inkjet used in home printers was developed independently by Canon and Hewlett-Packard in the late 1970s and reached consumers in the mid-1980s.

Can I use any brand of ink in my inkjet?

Use cartridges made for your printer model. Remanufactured and compatible cartridges work in most printers; just avoid firmware-locked plans like HP+ that require Original HP ink.

How long does an inkjet printhead last?

Printheads built into cartridges are replaced with every cartridge. Permanent printheads in Epson, Brother and some Canon and HP printers usually last the life of the printer if they're used regularly and not allowed to dry out.

Is a thermal inkjet the same as a thermal printer?

No. A thermal inkjet uses heat to fire liquid ink; a thermal printer uses heat on special paper or a ribbon with no ink at all. See what is a thermal printer?

Keep Your Inkjet Running

Whatever technology your printer uses, fresh ink keeps the nozzles happy. Look up your model on Find Ink by Printer, or shop HP, Canon, Epson and Brother ink cartridges.

Sources

• Wikipedia: Inkjet printing (thermal and piezoelectric drop-on-demand, history, droplet volumes)
• Epson: Micro Piezo technology
• Epson Europe Knowledge Base: Micro Piezo vs. thermal printing technology