Start with the question the prototype must answer
A prototype is a test. Before choosing a printing process, decide what the part needs to prove. Is it checking how a product looks in the hand? Whether a snap fit holds? Whether a bracket clears its neighbours? Whether twenty units can be handed to testers next week?
SLA, SLS and MJF answer those questions differently. All three are mature, widely available processes, and all three can produce good prototypes. The best choice depends on the property you are testing, not on which machine is newest.
How each process works, in brief
SLA (stereolithography)
A laser or projected light cures liquid resin one thin layer at a time. Parts are built on supports, which are removed afterwards, and are then washed and post-cured with UV light. Layers are typically around 0.025–0.1 mm thick, so surfaces are smooth and fine details come out sharp.
SLS (selective laser sintering)
A laser fuses nylon powder, layer by layer, in a heated bed. The surrounding powder supports the part, so no support structures are needed. Layers are typically around 0.1 mm. Parts come out with a slightly grainy, matte surface and are tough enough for functional testing.
MJF (Multi Jet Fusion)
A print head deposits fusing and detailing agents onto a bed of nylon powder, and infrared energy fuses the treated areas, one layer at a time. Like SLS, the powder supports the parts. Layers are typically around 0.08 mm. Parts are usually grey as printed and are often dyed black. Properties are broadly similar to SLS nylon.
Side-by-side comparison
| Property | SLA | SLS | MJF |
|---|---|---|---|
| Typical materials | Standard, tough, clear, flexible and high-temperature resins | PA12, PA11, glass-filled PA | PA12, PA11, glass-filled PA, TPU |
| Typical layer height | ~0.025–0.1 mm | ~0.1 mm | ~0.08 mm |
| Surface as printed | Smooth; support marks on one side | Matte, slightly grainy | Matte, slightly grainy, often dyed |
| Supports | Required | Not required | Not required |
| Typical minimum wall | ~0.5–1.0 mm | ~0.7–1.0 mm | ~0.7–1.0 mm |
| Typical accuracy | Around ±0.1–0.2 mm on small parts | Around ±0.3 mm on small parts | Around ±0.3 mm on small parts |
| Toughness | Brittle to moderate, grade dependent | Good | Good |
| Long-term stability | Some resins creep or yellow with UV | Stable | Stable |
| Transparent parts | Possible with clear resin and finishing | No | No |
Accuracy figures above are typical starting points for small parts. Larger parts, thin walls and unsupported spans all reduce accuracy, and results vary between machines and materials.
Choosing by what you are testing
Appearance and ergonomics
For models that people will look at and hold, SLA is usually the first choice. The smooth surface takes paint well, fine text and edges stay crisp, and clear resins can show internal parts or light pipes. Plan for support marks on one side; ask for the cosmetic face to be oriented away from the supports.
Snap fits, hinges and functional tests
For parts that flex, clip together or take knocks, nylon from SLS or MJF is the safer choice. PA12 tolerates repeated bending far better than most resins, which makes it suitable for living hinges and snap-fit trials. Expect the surface to feel slightly sandy; it can be smoothed by tumbling or vapour treatment if needed.
Fit checks and assembly trials
For checking that parts fit together, all three processes work. SLA gives the closest detail; nylon parts are tougher if they will be assembled and disassembled many times. Leave clearance between mating printed parts. Around 0.2–0.5 mm is a typical starting point, depending on size and process.
Small batches for testers
When you need many small parts at once, powder processes have an advantage. Parts can be nested throughout the build volume rather than only on a build plate, so a full build can carry many units. MJF is often chosen for consistent appearance across a batch, especially when dyed black.
Material notes for prototypes
Standard and tough resins
Standard SLA resins give the best detail but can be brittle, so thin clips may snap on the first assembly. Tough or durable resins trade a little detail for much better resistance to cracking and are a good default for functional SLA parts.
High-temperature and clear resins
High-temperature resins hold their shape near hot components or in short heat tests. Clear resins need sanding and lacquer to become truly transparent; as printed they look frosted.
PA12 and PA11
PA12 is the general-purpose nylon for SLS and MJF, with good stiffness and dimensional stability. PA11 is somewhat more flexible and impact resistant, which helps with hinges and parts that see repeated bending.
Filled and flexible grades
Glass-filled nylon adds stiffness and heat resistance but reduces toughness. TPU on powder systems gives rubber-like parts for seals, grips and bumpers.
Orientation, shrinkage and timing
Every printed part has a build direction, and properties are slightly different along it. SLA parts are strongest within each layer; powder parts are closer to uniform but still benefit from thoughtful orientation. Flat, thin panels in powder processes can warp as they cool, so ribs or a slight curve help keep them flat.
Allow time for post-processing when planning a test schedule. SLA parts need washing, support removal and UV curing. Powder parts need to cool in the bed before they are removed and cleaned, which adds time after printing ends. Painted or smoothed parts add further steps. For a design review on a fixed date, mention the date when requesting the parts so the process and finish can be chosen to suit it.
Design tips that apply to all three
- Keep walls above the typical minimum and avoid long, thin unsupported features
- Add fillets where walls meet; sharp internal corners concentrate stress
- Hollow large solid sections and add escape holes so resin or powder can be removed
- Orient holes and critical features so they are accurate in the build direction you choose
- Model threads only for coarse sizes; for fine threads, use inserts or tap after printing
- State which faces are cosmetic so the build orientation can favour them
Finishing options
| Finish | SLA | SLS / MJF | Notes |
|---|---|---|---|
| Support removal and sanding | Standard | Not needed | Support nubs sanded on SLA parts |
| Bead blasting | Optional | Standard | Removes loose powder; even matte look |
| Dyeing | Not typical | Common (black) | Uniform color through the surface layer |
| Primer and paint | Very good | Good after smoothing | Best route to a production-like look |
| Vapour or chemical smoothing | Not typical | Available | Seals and smooths nylon surfaces |
| Threaded inserts | Possible | Common | Heat-set inserts work well in nylon |
When printing is not the best prototype
If the prototype must be made from the production material, or must hold tight tolerances, consider other routes. CNC machining can produce prototypes in real aluminum, steel or engineering plastics. Urethane casting can produce small batches of ABS-like or rubber-like parts with good cosmetic surfaces from a silicone mold. These options cost more per part at very low quantities but answer questions printing cannot, such as how a specific grade behaves under load.
Practical decision guide
- Need a smooth, detailed or transparent model? Choose SLA.
- Need tough parts that flex, clip or take knocks? Choose SLS or MJF nylon.
- Need many small, consistent parts quickly? MJF or SLS, nested in one build.
- Need the production material or tight tolerances? Consider CNC machining or urethane casting.
Next steps
Upload STL, 3MF or STEP files through the quote form and choose a process per part, or leave a note describing what the prototype has to prove. The reviewing engineer will recommend a process, orientation and finish before pricing.