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Now you know how 3D printers work!

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Try it yourself ↓

How do 3D printers work?

▶ 4:29 video · Watch on YouTube

  1. 0:00 Start
  2. 0:29 Slice it like bread
  3. 1:13 A robot glue gun
  4. 2:01 Thin or thick?
  5. 2:40 Honeycombs and helpers
  6. 3:24 Beyond plastic string

Your turn

Run the printer yourself

Play with the printer!

Each lab is one step from the video. Slice, draw, slide and switch, and see what happens.

Each lab isolates one idea. The models are simplified and not to scale.

Tap the buttons and slide the sliders.

1

Slice the boat

Slice the model

Slice the boat

Drag the blue slice up the boat. How does the layer shape change?

Every cross-section becomes its own toolpath: walls plus infill.

Slide it up and down. Look at each slice!

▶ Watch this part
2

Draw a layer

Trace a toolpath

Draw a layer

Draw a layer, then drop the bed for the next one.

The hot end traces X–Y; the bed steps down in Z.

Tap Draw layer. Then tap Next layer.

▶ Watch this part
3

Thin or thick?

Layer height trade-off

Slide the layer height. What happens to the time and the smoothness?

Layers = height ÷ layer height; time scales roughly with the layer count.

Steps are drawn 12× thicker than real, and times are simplified.

▶ Watch this part
4

Supports and infill

Supports and infill

Helpers and honeycombs

Switch supports and infill on and off. What happens to the sail, the plastic and the time?

Supports rescue overhangs; infill trades material and time for strength.

Tap Supports. Does the sail still droop?

▶ Watch this part
5

Three kinds of printer

Three process families

Three kinds of printer

Switch between the printers. How does each one build a layer?

Extrusion, vat photopolymerisation and powder bed fusion, side by side.

Tap each printer. Watch it build!

▶ Watch this part

How does a 3D printer work?

A 3D printer makes a real thing, like a toy boat, one thin layer at a time. It starts with a long coil of plastic string.

1. Slice it like bread

First, someone draws the boat on a computer. Then the computer cuts it into lots of thin, flat slices, like bread. It makes a path for each slice.

2. A careful glue gun

The printer works like a very careful hot glue gun. It melts the plastic string and draws one flat slice with a thin line. The line cools and sticks. Then the printer draws the next slice on top.

3. Helpers and honeycombs

Plastic can't sit on thin air, so the printer adds helpers under parts that stick out. You snap them off at the end. Inside, many prints are not solid. They are full of little rooms, for example in a grid or honeycomb pattern.

Stay safe! The nozzle gets very hot and can burn you. Always print with a grown-up, in a room with fresh air, and keep your fingers away from the moving nozzle.
Did you know? Astronauts have used a 3D printer on the space station to make a tool!

← More explainers

How do 3D printers work? The short answer

A 3D printer builds an object one thin layer at a time. That's why it's also called additive manufacturing: it adds material only where it's needed, instead of cutting a shape out of a bigger block.12 First, software cuts a 3D computer model into hundreds of flat slices and turns each slice into a path. Then the printer follows those paths, layer on layer, until the object is finished.58

Most home and school 3D printers work like a very precise, robot-controlled hot glue gun. They melt a thin plastic string called filament in a hot nozzle and draw each layer with a line of soft plastic. The line cools almost at once and sticks to the layer below.1

What is a 3D printer?

A 3D printer is a machine that turns a digital 3D model into a real, solid object. A normal inkjet printer puts dots of ink on paper where a picture needs them. A 3D printer does the same thing with material, and then it keeps going upwards, stacking two-dimensional layers into a three-dimensional shape.16 Printers can build with plastic, metal, ceramics, and even concrete or food.15

How does a 3D printer work, step by step?

  1. Design a model. Someone draws the object in computer-aided design (CAD) software or downloads a ready-made model. Doctors can even start from a medical scan such as an MRI.13
  2. Slice it. A program called a slicer cuts the model into a stack of thin, flat layers and describes each layer as a set of moves for the nozzle. It saves those moves, along with settings such as the nozzle temperature, as G-code.810
  3. Prepare the printer. Load the filament and make sure the build plate is clean, so the first layer sticks and the print doesn't warp or slide.1
  4. Print layer by layer. The printer melts the material and draws the first layer. Then the platform moves down (or the nozzle moves up), and the next layer begins. This repeats hundreds or thousands of times.15
  5. Finish it. Peel the object off the plate, snap off any supports, and sand or clean it if needed.1

A print can take anywhere from a few minutes to several days, depending on how big and complicated the object is.1

What does a slicer do?

The slicer is the translator between your model and the machine. It takes a 3D model file (often an STL file) and turns it into printer commands in G-code.8 Think of slicing a loaf of bread: each slice of the toy boat in our explainer is just a flat shape. Near the bottom it's the outline of the hull, and higher up it's a tiny ring where the mast is. For every slice, the slicer plans an outer wall, an inner wall and a fill pattern, and writes them as a path, line by line, like G1 X12.4 Y3.1, which means "move in a straight line to this spot."89

The slicer also makes the big choices for you: how thick each layer is, how much of the inside to fill, and where to add supports. Many slicers show a layer-by-layer preview before you print.10

How does the nozzle melt and lay down plastic?

This process is called material extrusion (you'll also see it called fused deposition modelling, FDM, or fused filament fabrication, FFF). It's the most common kind of desktop 3D printing.1 A motor pushes filament into the hot end: a heated metal block with a small nozzle at the bottom. The nozzle opening is usually between 0.3 and 1.0 millimetres wide, and a temperature sensor keeps the heat steady.9

A popular filament is PLA (polylactic acid). It's a bioplastic made from lactic acid, which microbes produce by fermenting plant sugars and starches.7 PLA melts at about 170–180 °C, and research labs print it with the nozzle at about 200–220 °C.131920 (For more on where plastics come from, see how plastic is made.)

Motors slide the nozzle across the build plate in two directions, X and Y, while soft plastic squeezes out as a thin bead. The bead hardens quickly and bonds to the layer underneath. When a layer is done, the platform drops (or the nozzle rises) in the Z direction, and the next layer starts.19 Those motor moves are controlled by a small computer inside the printer, following the G-code line by line. (Curious what's going on inside computers? See how computers work.)

Layer height: speed versus smoothness

Layers are often about 0.1 millimetres thick, and home printers commonly use layer heights between about 0.1 and 0.3 mm.112 The number of layers is simple arithmetic: object height ÷ layer height.

Layer heightLayers for a 6 cm toy boatRough print timeSurface
0.3 mm200fastestvisible "staircase" steps on curves
0.2 mm3001× (baseline)good balance
0.1 mm600about 2× longersmoothest

Why the steps? Every layer is flat, so a sloped or curved surface ends up as a tiny staircase. Research on printed PLA found that layer height is one of the most important settings for how rough the surface feels.12 Thinner layers make the stairs smaller, but you need more of them, so the print takes longer. The time estimates in the table are simplified: real prints also depend on speed, walls and infill.

Supports and infill: the slicer's two secret tricks

Supports. A printer builds from the bottom up, so every new layer has to rest on something. A small overhang can lean on the layer beneath it, but a part that sticks far out sideways would droop into thin air.9 So the slicer adds supports: a thin scaffold, often a zig-zag lattice or a tree shape, that holds up overhangs and snaps off when the print is done. Tree supports are usually easier to remove and use less filament.81

Infill. Many 3D prints are not solid. The slicer prints solid outer walls and fills the inside with a light internal pattern called infill, which saves plastic and time. You can choose the infill density: more for a strong part, less for a quick model.8 Slicers offer several ready-made patterns, and a honeycomb is one that researchers test for strength.21 There's a neat bit of maths behind it too: hexagons split a flat area into equal cells using the least total wall length.14

Types of 3D printers

Standards group ASTM sorts additive manufacturing into seven categories.1 Here are the three you'll hear about most:

TypeHow it builds each layerGood for
Material extrusion (FDM/FFF)Melted plastic squeezed from a moving hot nozzleHome and school printers, prototypes
Vat photopolymerisation (e.g. SLA, "resin")Ultraviolet laser or projector light hardens a thin layer of liquid resinVery fine detail; it's the oldest type of 3D printing
Powder bed fusion (e.g. SLS)A laser or electron beam melts or fuses a thin layer of plastic or metal powder; then fresh powder is spread on topStrong nylon and metal parts, medical devices

The other categories include binder jetting (glue sprayed onto powder), material jetting (inkjet-style heads), directed energy deposition (a laser melting wire or powder as it's laid down) and sheet lamination (bonding thin sheets).15

What can you make with a 3D printer?

The biggest use is rapid prototyping: quickly making test versions of parts that will later be mass-produced another way.5 But printed parts are showing up in more and more finished products:

  • Medicine: skull plates and hip implants, surgical guides, dental crowns and external prosthetic hands. Some devices are patient-matched, meaning they're made from one person's scan.34
  • Rockets: NASA printed a rocket engine injector with 40 spray elements as a single part, and a printed turbopump needed 45% fewer parts.1516
  • Space: the first 3D printer on the International Space Station, in 2014, was a filament printer. It worked normally in microgravity, and one of its first prints was a wrench whose design was sent up from the ground.17
  • Buildings: researchers print concrete blocks, and in NASA's 3D-Printed Habitat Challenge (finished in 2019) teams used machines to print one-third-scale habitats automatically.518 In 2025 the U.S. Army opened barracks at Fort Bliss, Texas, that were printed from a concrete-based material: the design was sliced into horizontal layers and built up layer by layer.22

Because 3D printing only puts material where it's needed, some processes use about 98% of the raw material in the finished part.1 It has limits too: it's slow, parts are usually less precise and smooth than machined ones, and the choice of materials and part sizes is limited.5

Who invented 3D printing?

Engineer and physicist Chuck Hull invented 3D printing in the 1980s.1 The name "3D printing" first described one specific powder-and-binder process patented at MIT in 1993. Today it's used for all additive manufacturing methods.5

Is 3D printing safe?

With sensible care, yes. The nozzle and heated parts get hot enough to burn, and melting plastic releases fumes. Safety guidance from NIOSH suggests good ventilation and protection, such as thermal gloves, around hot print heads.11 For kids: print with an adult, in a room with fresh air, and keep your fingers away from the moving nozzle.

Common misconceptions

"A 3D printer makes the whole object at once." It builds one thin layer at a time; a filament printer draws each layer line by line.15
"3D prints are solid plastic." Most have solid walls around a light infill pattern inside.8
"Thinner layers are always better." They're smoother, but they take longer because there are more of them.12
"3D printers only melt plastic." Others harden liquid resin with light, fuse metal powder with lasers, or lay down concrete.15
"You can print any shape in mid-air." Big overhangs need supports underneath them.89

FAQ

How does a 3D printer work in simple terms?

Software slices a 3D model into hundreds of thin flat layers and turns each one into a path. The printer then builds the object one layer at a time. A home printer does this by melting plastic filament in a hot nozzle and drawing each layer on top of the one before. Resin printers work differently: they use light to harden a thin layer of liquid resin at a time.

What is needed to use a 3D printer?

A 3D model file (designed in CAD software or downloaded), slicer software that turns the model into G-code instructions, the printer itself, and printing material such as a spool of PLA filament. The build plate also has to be clean and level so the first layer sticks.

How long does it take to 3D print something?

Anywhere from minutes to days. It depends on the object's size and complexity, and on settings such as layer height: halving the layer height roughly doubles the number of layers, and so roughly doubles the print time.

Are 3D printed objects solid?

Usually not. The slicer prints solid outer walls and fills the inside with a lighter pattern called infill, for example a grid or honeycomb. Infill density can be changed to trade strength against plastic and time.

What can you make with a 3D printer?

Prototypes of new products, toys, spare parts and tools, and in industry and medicine: dental crowns, hip and skull implants, prosthetic hands, surgical guides and rocket engine parts. Builders and researchers also print concrete blocks and walls (the U.S. Army has 3D-printed concrete barracks), car bodies and food.

Who invented 3D printing?

Engineer Chuck Hull invented 3D printing in the 1980s. The name '3D printing' first described a specific powder-and-binder process patented at MIT in 1993, and is now used for all additive manufacturing processes.

Is 3D printing safe for kids?

With care. The nozzle and heated parts get hot enough to burn, and melting plastic gives off fumes, so kids should print with an adult, in a well-ventilated room, and keep their hands away from the print head while it runs.

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Sources

  1. U.S. Department of Energy, How 3D Printers Work
  2. NIST, What is additive manufacturing?
  3. U.S. FDA, 3D Printing of Medical Devices
  4. U.S. FDA, Medical Applications of 3D Printing
  5. Encyclopaedia Britannica, 3D printing
  6. Encyclopaedia Britannica, How Do 3D Printers Work?
  7. Encyclopaedia Britannica, Bioplastic (polylactic acid)
  8. Wikipedia, Slicer (3D printing) (citing Evans, Practical 3D Printers, 2012, and Kloski, Getting Started with 3D Printing, 2016)
  9. Wikipedia, Fused filament fabrication
  10. NC State University Libraries, Slicer software guide
  11. CDC / NIOSH, 3D Printing with Filaments: Health and Safety Questions to Ask (2020)
  12. Pérez et al., Surface Quality Enhancement of FDM Printed Samples, Materials (2018)
  13. Baran & Erbil, Surface Modification of 3D Printed PLA Objects by FDM: A Review, Colloids and Interfaces (2019)
  14. Wikipedia, Honeycomb theorem (proof: T. C. Hales, 2001)
  15. NASA, Sparks Fly as NASA Pushes the Limits of 3-D Printing Technology
  16. NASA Technical Reports Server, Additive Manufacturing for Affordable Rocket Engines (2016)
  17. NASA, Solving the Challenges of Long Duration Space Flight with 3D Printing
  18. NASA, 3D-Printed Habitat Challenge
  19. Study of Material Color Influences on Mechanical Characteristics of FDM Parts, Materials (2022) (PLA printed at 200 °C)
  20. Optimization of Deposition Temperature and Gyroid Infill of PLA, J. Manuf. Mater. Process. (2025) (PLA printed at 200 and 220 °C)
  21. On Strength Variations Effected by Infill Patterns Such as Honeycomb, Gyroid, and Archimedean Chords, Polymers (2026)
  22. U.S. Army, Army opens DOD's first 3D-printed barracks (2025)