FDM vs. SLS
Choose filament extrusion or polymer powder-bed fusion from the loaded geometry, named material, support and cleaning route, finish, inspection and batch plan.
The geometry and delivery route decide before a process label does
FDM deposits thermoplastic roads and may add removable support. SLS fuses polymer powder while surrounding powder supports each layer. That difference changes orientation, internal access, surface state and batch planning.
FDM
FilamentA heated nozzle lays down thermoplastic, one toolpath at a time.
Design check: Plan layer direction and access to remove supports.
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.
FDM
Use deliberate toolpaths and orientation
Screen FDM when a compatible filament, sparse or solid interior, accessible support plan and direction-aware load path suit the part.
SLS
Use the powder volume
Screen SLS when unsupported undercuts, nested parts or consolidated polymer geometry justify cooling, depowdering and a powder-bed surface.
Either
Qualify the delivered part
The process name does not establish strength, fit, sealing or life. Keep the material product, machine, orientation, conditioning, finish and test with the result.
Support removal and powder removal create different design limits
FDM supports must be avoided, broken away or dissolved. SLS normally avoids attached supports, but every enclosed path still needs a credible way to remove unfused powder.
| Feature | FDM review | SLS review |
|---|---|---|
| Loaded wall or arm | Align toolpaths and layer direction with the load; inspect the sliced wall and any seam. | Review build direction, thermal distortion and the named powder data for the loaded direction. |
| Overhang or undercut | Place supports where they can be removed without damaging the functional face. | No attached support is normally needed, but down-facing texture and local thermal behavior still need review. |
| Internal channel | Confirm the slicer can form the roof and that support or wash solution can leave the channel. | Provide powder escape and cleaning access through bends, branches and blind volumes. |
| Assembly clearance | Test the chosen printer, material, orientation and support condition with a representative coupon. | Test the chosen powder, orientation, cooling and finish; loose powder must not mask interference. |
| Batch nesting | Compare part-by-part toolpaths, changeover and support labor for the actual build. | Compare three-dimensional packing with cooling, breakout and depowdering for the actual batch. |
Compare named thermoplastic routes instead of family labels
Filament and powder with similar polymer names are different commercial products processed on different systems. Use each manufacturer data sheet only within its printer, build and conditioning scope.
| Candidate | Why it may enter the comparison | Evidence to keep |
|---|---|---|
| Stratasys ULTEM 9085 filament | An industrial FDM candidate when its documented flame, smoke, toxicity or thermal scope matches the requirement. | Printer compatibility, orientation, build parameters, conditioning and the applicable specification. |
| Formlabs Nylon 12 Powder | A balanced SLS nylon candidate for functional prototypes or end-use geometry. | Fuse system, powder refresh and atmosphere guidance, orientation, conditioning and finish. |
| EOS PA 2200 | A distinct PA12 SLS product with its own supported systems and published process evidence. | Exact system and parameter set, powder handling, direction, condition and test method. |
| Formlabs Nylon 11 Powder | A separate SLS candidate when ductility or impact-oriented behavior matters. | Do not transfer PA12 data; validate the loaded feature and conditioning state. |
These examples show the level at which a comparison becomes useful. Browse the 3D printing material library for documented alternatives; availability is confirmed with the quote.
Plan cleanup before promising appearance or fit
FDM begins with layer roads and possible support scars. SLS begins with a powder-bed texture and residual powder. Abrasion, smoothing, dye, paint or machining can change edges and dimensions in either route.
- Map witness surfaces. Mark where an FDM seam or support and an SLS down-facing or breakout surface may appear; keep critical datums out of uncontrolled cleanup zones.
- Name the complete finish. Specify blasting, dyeing, smoothing, coating or local machining by material and acceptance state. A generic “smooth” note is not inspectable.
- Inspect after finishing. Measure bores, clips, sealing faces and assembly gaps after every operation that removes or adds material.
Use the FDM design guide, SLS design guide and surface-finish selection guide to define the candidate routes.
Run one comparison that can answer the design question
Build the same controlling feature in each eligible material, then test both in their delivered condition. A useful sample represents the load direction, support or powder access, finish and inspection method of the production part.
| Record | FDM sample | SLS sample |
|---|---|---|
| Build identity | Printer, nozzle or extrusion setup, layer strategy and orientation | Printer, powder product, parameter set, refresh/atmosphere scope and orientation |
| Delivered state | Support removal, conditioning, smoothing/coating and machining | Cooling, depowdering, blasting, dye/smoothing/coating and machining |
| Acceptance test | Critical dimensions plus the relevant load, heat, fluid or cycle test | The same functional test and dimensional inspection in the same service condition |
| Decision | Pass/fail reason and any geometry change needed | Pass/fail reason and any cleaning, finish or geometry change needed |
Frequently asked questions
Is SLS stronger than FDM?
There is no universal strength ranking. Compare named material products with their machine, orientation, conditioning, finish and test method, then test the actual load path.
Does SLS need support structures?
Surrounding powder normally supports SLS geometry without attached supports. The part still needs powder escape, depowdering access, cooling control and inspection of affected surfaces.
Is FDM always better for a single prototype?
No. Part size, filament qualification, support labor, geometry, finish and the purpose of the prototype can change the choice. Compare delivered parts against the same acceptance plan.
Can the same nylon specification be used for FDM and SLS?
A shared polymer family name does not make the products equivalent. Filament and powder products use different formulations and processes, so each needs its own qualified data and validation.
Sources and further reading
- Formlabs — FDM, SLA and SLS technology comparisonManufacturer overview of mechanisms, support workflows, materials and post-processing; example timing is system- and build-specific.
- Stratasys — FDM technologyExtrusion mechanism and support workflow.
- Stratasys — FDM support materialsBreakaway and soluble support compatibility is model-material specific.
- Formlabs — Nylon 12 PowderNamed SLS product and printer/workflow scope.
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.