Guide
FDM vs SLA vs SLS: Which 3D Printing Process Should You Order?
By the Triiidiii editors · Updated
When you upload a file to a 3D printing service, the first choice is the process. FDM, SLA and SLS are the three you will see everywhere. They build parts in very different ways, so the same model comes out with a different finish, strength and price from each. Here is how they compare and how to choose.
Side by side
| FDM | SLA | SLS | |
|---|---|---|---|
| How it works | Melts plastic filament and lays it down in lines | Cures liquid resin with a laser (DLP: a projector) | A laser fuses nylon powder, layer by layer |
| Detail | Lowest; layer lines are visible | Highest; fine features and sharp edges | Good; slightly soft edges |
| Surface | Ridged layer lines | Smooth | Matte, slightly grainy |
| Strength | Good along layers, weaker between them | Depends on the resin; standard resin is brittle | Strong and even in all directions |
| Supports | Needed for overhangs; leave marks | Needed; leave small marks to sand off | None; the powder holds the part |
| Typical materials | PLA, PETG, ABS, ASA, TPU | Standard and engineering resins | Nylon PA12, PA11, TPU |
| Usually best for | Cheap prototypes, large simple parts | Small detailed parts, visual models | Functional parts, complex shapes, small batches |
FDM: fused deposition modeling
FDM is the process most desktop printers use. A heated nozzle extrudes a thin bead of plastic and traces each layer. It is usually the cheapest way to get a part, and it handles large parts well.
The trade-offs: layer lines are visible, small details soften, and parts are weakest between layers, so a bracket printed lying down may be stronger than the same bracket printed standing up. Overhangs need support structures, which leave marks where they are removed.
Choose FDM for early prototypes, jigs and fixtures, large simple parts, and anything where price matters more than looks.
SLA: stereolithography (and DLP)
SLA uses light to harden liquid resin one thin layer at a time. DLP and LCD printers work the same way with a projector or screen instead of a laser. The result is the finest detail and smoothest surface of the three, which is why it is popular for miniatures, dental and jewelry models, and visual prototypes.
The trade-offs: standard resins can be brittle, parts need supports and post-curing, and build sizes are often smaller. Engineering resins are tougher or more heat-resistant, at a higher price.
Choose SLA for small, detailed parts, smooth visual models, and molds or patterns.
SLS: selective laser sintering (and MJF)
SLS spreads a thin layer of nylon powder and fuses the cross-section with a laser, layer after layer. The unfused powder supports the part, so no support structures are needed, and moving parts and interlocking shapes can be printed in one go. HP's Multi Jet Fusion (MJF) is a related powder process with similar uses.
The trade-offs: the surface is matte and slightly grainy, and parts usually come out gray or white unless dyed. Hollow parts need escape holes so the powder can be removed.
Choose SLS or MJF for strong functional parts, complex geometry, snap fits and hinges, and small production runs.
Other processes you'll see
- Metal printing (SLM, DMLS, binder jetting): metal parts in stainless steel, aluminum, titanium and more. Far more expensive.
- Material jetting and PolyJet: jets droplets of photopolymer; can mix colors and materials in one part.
- Full-color processes: some services print in full color, for example in nylon or resin, for figures and models.
A quick way to decide
- Is it mainly for looks and small? SLA.
- Does it have to take loads, flex or snap? SLS or MJF nylon.
- Is it large, simple or a first draft? FDM.
- Does it have to be metal? Metal printing, or casting for jewelry.
Then pick a material with our materials guide, and see which services offer that process in our comparison.