SLA vs. SLS
Choose cured-resin SLA or nylon powder-bed SLS by the real requirement: feature detail, support strategy, material behavior, powder escape, finish and intended service.
SLA and SLS solve different part problems
SLA is a light-cured resin process. SLS fuses thermoplastic powder. A smooth surface or support-free build alone is not enough to select one; start with the part’s material, mechanism and finished state.
SLA
Liquid resinLight cures resin into a solid layer. A bottom-up system is shown here.
Design check: Plan support contacts, washing and the specified cure.
SLS
Polymer powderA laser scans and fuses selected regions of a powder layer.
Design check: Loose powder supports the part; cavities need a removal path.
Process principles shown in cutaway. Energy colours are schematic. Supports, hardware and layer thickness are simplified; machine configurations vary.
SLA
Detail and surface
Screen for fine features, patterns, visual prototypes and specialized cured resins when washing, support removal and post-cure are acceptable.
SLS
Nylon function and complexity
Screen for complex PA11, PA12, filled-nylon or TPU geometry when powder escape, surface texture and material orientation are designed in.
Material first
Do not compare family names
A tough resin and PA12 may both be useful, but their conditioning, aging, finish, ductility and test evidence are not interchangeable.
Use the geometry and service condition to break the tie
SLA’s attached supports and SLS’s loose powder create distinct design tasks. Both need a planned post-processing and inspection route.
| Decision area | SLA | SLS |
|---|---|---|
| Fine detail | Often a strong candidate for small detailed surfaces and patterns. | Can produce detail, but powder particle size, thermal history and finishing influence the result. |
| Supports / cleanup | Attached supports need placement and removal; wash and post-cure complete the route. | Surrounding powder supports the build, but enclosed volumes and mechanisms need powder escape. |
| Functional polymer | Choose a resin formulation and post-cure for the service requirement. | Choose a named PA11, PA12, filled nylon or TPU product and review orientation/conditioning data. |
| Internal cavities | Need drainage and cleaning for liquid resin plus post-cure access. | Need accessible pathways and openings to remove unfused powder. |
| Surface / finish | Can begin with a smooth surface; supports and coatings still affect visible faces. | Has a powder-bed surface that can be blasted, dyed, smoothed or coated subject to material/process compatibility. |
| Flexible mechanism | Evaluate the named flexible resin and cure state. | Evaluate the named PA11 or TPU powder, orientation and repeated-deflection evidence. |
A hollow CAD model needs a cleanable manufacturing path
The word “hollow” hides two different problems: uncured resin in SLA and unfused powder in SLS. Both can affect mass, cleanliness, appearance and function.
A sealed cavity retains material
Hollow geometry does not guarantee a hollow delivered part. Unfused powder, liquid resin or support can remain inside.
Design a cleaning route
Provide accessible openings and a path through the cavity. Opening size depends on process, material, channel length and cleaning method.
Schematic illustrations; not to scale. Confirm the design for the chosen material, process and final use.
- Map the liquid or powder path. Check branches, blind pockets and trapped volumes—not only the drain hole at the outer shell.
- Specify cleanliness when it matters. A fluid path, optical enclosure or medical-development component needs a defined acceptance condition, not a generic “cleaned” note.
- Do not use hollowing to hide a weak shell. The wall must still survive handling, finishing and service loading.
Compare the material behavior you will actually use
A nylon powder and an engineering resin can each be suitable. The correct comparison is a named product and condition against the requirements, not an assumed “production-grade” label.
The polymer name is a starting point
A material family can contain multiple formulations. Check the commercial product, process and test condition.
Fillers change the trade-off
Glass beads, glass fibres and carbon fibres are distinct reinforcements. Compare stiffness, elongation, surface and directionality together.
Schematic illustrations; not to scale. Confirm the design for the chosen material, process and final use.
| Requirement | Evidence to request | Why it matters |
|---|---|---|
| Load and deflection | Material product, orientation and conditioning data | A tensile number does not define a snap, hinge, threaded boss or impact event. |
| Heat and chemicals | Specific test medium, temperature, duration and load | Family-level statements are not the same as service qualification. |
| Appearance | As-built surface, visible faces and finish sample | SLA support marks and SLS texture demand different remedies. |
| Traceability / compliance | Material lot and test scope requested before ordering | Material documentation does not establish finished-part certification. |
Choose the sample that can fail usefully
For SLA, inspect after wash, cure and finish. For SLS, inspect after depowdering and chosen finish. Use the same test plan so the result is a comparison, not two unrelated prototypes.
Learn from a first article
Use representative geometry, material and finishing to verify the properties that matter before repeating the order.
Control the production recipe
Record material product, build settings, orientation, finishing and inspection criteria. Confirm changes before the next batch.
Schematic illustrations; not to scale. Confirm the design for the chosen material, process and final use.
Continue to the SLA design guide or SLS design guide for route-specific geometry checks. For nylon product selection, use the material library.
Frequently asked questions
Is SLS stronger than SLA?
Neither process is categorically stronger. SLS commonly offers thermoplastic nylon options, while SLA offers many resin formulations. Compare the named product, orientation, cure or conditioning, geometry and service condition.
Does SLS need supports?
SLS powder supports the build, so it normally avoids attached supports. The trade-off is depowdering: internal cavities, channels and moving features need an accessible cleaning route.
Which is better for smooth cosmetic parts?
SLA is often screened first because it can provide fine detail and a smooth as-built surface. Confirm the resin, support locations, finishing and durability rather than using surface appearance as the only criterion.
Can either process make watertight parts?
That depends on geometry, material, orientation, cleaning, finishing and the medium and pressure involved. Define a leakage test for the finished part instead of inferring sealing performance from the process name.
Sources and further reading
- Formlabs — FDM, SLA and SLS technology comparison
- Formlabs — watertight 3D printing guideWater-tightness evidence is material, process and geometry dependent.
Specify the details that make the part work.
Upload your CAD and drawing with the material, quantity, finishing and critical dimensions. Confirm the manufacturing route before production.