3D Printing
SLA vs SLS vs FDM: Choosing a 3D Printing Process
Resolution, strength and cost pull in different directions. Match the process to what the part must do.
Key takeaways
- SLA gives the smoothest surface and fine detail, but brittle parts.
- SLS gives tough, functional nylon parts with a matte finish.
- FDM is the cheapest and fastest, with visible layer lines.
- Pick by function: look, strength or budget.
The short answer
Need a smooth visual model with fine detail? SLA. Need a tough bracket you can bolt on and drop? SLS. Need a cheap check part today? FDM.
Most projects use two of the three at different stages, not one forever.
How each process works
SLA: resin and light
A laser or projector cures liquid resin layer by layer. The layer height can be as fine as 0.05 mm, so the surface comes out smooth and detail holds well.
Parts are brittle compared with nylon. They also age in sunlight unless the resin is formulated for it.
SLS: powder and heat
A laser sinters nylon powder into solid geometry. No support structures are needed, because the surrounding powder holds the part up. That means you can nest many parts in one build.
Parts are tough, slightly porous and have a uniform matte finish.
FDM: filament and a nozzle
Thermoplastic filament is melted and extruded along a path. It is the most common desktop process and the cheapest per part.
Layer lines are visible, and strength depends heavily on print orientation.
Side by side
| SLA | SLS | FDM | |
|---|---|---|---|
| Resolution | 0.05 to 0.1 mm | 0.1 mm | 0.1 to 0.3 mm |
| Surface | Smooth, can be clear | Matte, slightly grainy | Visible layer lines |
| Strength | Brittle | Tough, functional | Moderate, anisotropic |
| Heat resistance | Low to moderate | Moderate | Moderate to high |
| Support needed | Yes, removed by hand | No | Yes, often |
| Typical cost | Medium | High | Low |
| Lead time | 2 to 4 days | 3 to 6 days | 1 to 3 days |
| Best for | Looks, detail, molds | Functional parts, small batches | Cheap checks, large parts |
Material behaviour matters more than the process name
Two SLS parts in different nylons behave differently. A standard PA12 is tough and flexible. A glass-filled PA12 is stiffer but more brittle.
Ask for the actual material data sheet, not just the process name. Tensile strength, elongation at break and heat deflection temperature tell you how the part will behave.
How to decide
- Is it for looking at? SLA. Fine detail and a smooth surface sell the design.
- Is it for using? SLS in PA12. It survives drops, threads and screws.
- Is it for checking a fit? FDM. Cheap enough to print three versions.
- Does it need to be clear? SLA in clear resin, then polish.
- Is it larger than 300 mm? FDM, or plan to print in sections and bond.
Post-processing
- SLA parts need support removal, washing and final curing. Expect hand work.
- SLS parts come out of the powder bed and need bead blasting for a clean surface.
- FDM parts can be sanded, but layer lines are hard to remove completely.
- All three can be painted, though SLS needs a primer to fill the grain.
Common questions
Which process is strongest?
SLS in nylon is usually the toughest for functional parts. FDM can be strong in-plane but splits between layers.
Can I tap a 3D printed part?
In SLS nylon, yes, with a coarse thread and a slightly smaller pilot hole. In SLA resin, use a heat-set insert instead.
Is SLA good for a snap fit?
Usually not. Resin is brittle and snaps. Use SLS nylon for living hinges and snap features.
The bottom line
Choose by the job the part has to do. Print looks in SLA, function in SLS, and early fit checks in FDM. Then move to machining or molding when the design stops changing.