FDM vs SLA vs SLS vs MJF: Which Process to Use
Share
Most plastic 3D printing comes down to four processes. They differ in how the part is built, and that decides what it costs, how strong it is and what the surface looks like.
Comparison
| Process | How it works | Typical accuracy | Surface | Relative cost |
|---|---|---|---|---|
| FDM | Melted filament laid down line by line | ±0.5 mm or ±0.5% | Visible layer lines | Lowest |
| SLA | Liquid resin cured by a laser or projector | ±0.2 mm or ±0.5% | Smooth, fine detail | Low to medium |
| SLS | Nylon powder fused by a laser | ±0.3 mm or ±0.3% | Matte, white, can be dyed | Medium |
| MJF | Nylon powder fused by a print head and heat lamp | ±0.3 mm or ±0.3% | Matte, grey, usually dyed black | Medium |
Accuracy is whichever figure is larger. These are typical values; machines and materials vary.
FDM: cheapest and biggest
FDM printers push filament through a heated nozzle and draw each layer as a set of lines, usually 0.1 to 0.3 mm thick. Nothing else gets a part in hand as cheaply, and the price doesn't climb as steeply as the other processes when parts get large.
The weak spot is the bond between layers. A bracket printed standing up, with the load pulling the layers apart, can break at a fraction of the load the same bracket carries when printed flat. Orientation is part of the design. Overhangs past 45° need supports, and layer lines show on curved and sloped faces.
Material choice matters more than in any other process:
- PLA is stiff and easy to print but softens around 55 °C. Fine for models and fit checks, not for a car interior in summer.
- PETG is tougher and handles about 70 °C. A good default for fixtures and brackets.
- ABS and ASA handle about 90 to 100 °C. ASA holds up to sunlight, so it suits outdoor parts.
- Nylon is tough and wears well, and carbon-filled grades are much stiffer. Nylon absorbs moisture, which changes its properties.
- TPU is rubbery and flexible, for gaskets, bumpers and grips.
SLA: smooth and detailed
SLA cures liquid resin with a laser, or with a projector or screen in the related DLP and MSLA printers, in layers as thin as 0.025 mm. Surfaces come out smooth and detail stays sharp: small text, thin ribs and fine textures print cleanly. Resin is the usual choice for presentation models, master patterns for casting and small precise parts.
Overhangs need supports, and their contact points have to be sanded off. Standard resins are brittle and yellow under UV light, so they suit models more than working parts. Engineering resins close some of that gap: tough resins are made to behave like ABS or polypropylene, flexible resins like rubber, and high-temperature resins have heat deflection temperatures above 200 °C.
SLS and MJF: parts that have to work
Both fuse nylon powder, most often PA12, layer by layer. SLS traces each layer with a laser. MJF sprays a fusing agent onto the powder and passes a heat lamp over the whole layer. In both, the unfused powder holds the parts up as they print, so there are no supports and no support marks, and parts can be stacked in three dimensions to fill the build.
The result is a tough, slightly flexible part that's close to equally strong in every direction, with good resistance to oils and fuels. Snap fits and clips work well. That's why these two are the default for functional plastic parts and for batches, where one build can hold dozens or hundreds of small parts.
The differences between them are small. MJF parts come out grey and are usually dyed black. SLS parts come out white and can be dyed other colors. Both have a matte, slightly grainy surface, and both shrink a little as they cool, so large flat parts can warp.
Pick by the job
- Checking size and fit: FDM. Cheap, quick and good to about half a millimeter.
- Showing a client, or a pattern for casting: SLA.
- A clip, bracket, housing or duct that has to work: SLS or MJF, or FDM in nylon or PETG for one-offs.
- Ten to a few hundred small plastic parts: SLS or MJF.
- Rubber-like parts: TPU, or a flexible resin.
- Metal: laser powder bed printing, or CNC machining when the shape allows. See 3D printing vs CNC machining vs injection molding.
If you're unsure, send the file to our 3D printing service with a note on what the part has to do, and we'll recommend a process when we quote.