Not all 3D printing is the same. The three technologies you'll meet most often — FDM, SLA and SLS — produce parts that look, feel and perform in completely different ways. Picking the wrong one wastes money. Picking the right one can make a project.
Below is the same reasoning we run through when a file lands in our inbox: what the part has to survive, how it has to look, how many you need and when you need them.
FDM — Fused Deposition Modeling
A nozzle melts plastic filament and lays it down layer by layer, building the part from the bed up.
Best for: functional prototypes, large parts, jigs and fixtures, housings, anything that needs to be tough and cheap.
Materials: PLA, PETG, ABS, ASA, nylon, polycarbonate, and carbon- or glass-filled composites.
Typical layer height: 0.1–0.3 mm. Thinner layers mean finer detail and a longer print — a 0.1 mm part takes roughly three times as long as the same part at 0.3 mm.
What it's genuinely good at: cost per cubic centimetre. FDM is the cheapest way to turn a CAD file into a solid object, and the material list is the broadest of the three processes. If a part needs to be UV-stable, chemical-resistant or stiff, there is almost certainly an FDM filament for it.
Where it bites you:
- Visible layer lines. Fine on a bracket, wrong on a visible trim piece unless it gets sanded, filled and painted.
- Anisotropy. An FDM part is meaningfully weaker across the layers than along them — commonly 30–50% weaker in Z, depending on material and settings. Orientation is a design decision, not a print setting.
- Support scars. Overhangs need support, and the surfaces that touch it come out rougher.
- Warping on long flat parts, especially in ABS.
SLA — Stereolithography (and resin printing generally)
A UV light source cures liquid photopolymer resin one layer at a time.
Best for: visual prototypes, small detailed parts, badges and emblems, mould masters, dental and jewellery models.
Materials: standard, tough, flexible, castable, high-temp and dental resins.
Typical layer height: 0.025–0.1 mm — an order of magnitude finer than FDM.
What it's genuinely good at: surface finish and fine feature resolution. Text, knurling, factory grain texture and sharp edges survive. A resin part off the machine looks like an injection-moulded part; an FDM part never does without work.
Where it bites you:
- UV degradation. Most resins yellow and embrittle in sunlight. For anything living on a dashboard or outdoors, that matters — either pick a UV-stable resin, paint and clear-coat it, or use a different process.
- Post-processing is mandatory. Wash in IPA, post-cure under UV, remove supports, sand the support nubs. That labour is part of the price.
- Impact strength. Standard resin is brittle. "Tough" and "durable" resins improve it, but a resin part is still the wrong answer for something that gets levered, clipped and re-clipped.
- Build volume and cost. Resin is more expensive per litre than filament, and large resin parts get expensive fast.
SLS — Selective Laser Sintering
A laser fuses nylon powder inside a heated powder bed. The un-sintered powder around the part acts as its own support.
Best for: end-use mechanical parts, complex geometries, living hinges, snap fits, and small production batches.
Materials: PA12 nylon, glass-filled nylon, carbon-filled nylon, TPU.
Typical layer height: 0.1 mm, with near-isotropic strength — SLS parts are much closer to equally strong in all directions than FDM parts.
What it's genuinely good at: parts that have to work rather than pose. No supports means geometry that would be impossible or costly in FDM — internal channels, captive features, lattices, thin living hinges that flex thousands of cycles without cracking. Because the whole build volume can be packed with parts, SLS also scales well: 50 clips cost far less per unit than one clip.
Where it bites you:
- Surface finish is matte and slightly grainy. Pleasant, but not glossy without extra finishing.
- Minimum job cost. A powder bed has to be filled, heated and cooled whether you print one part or eighty. One-offs carry a surcharge.
- Lead time. Print, then a slow controlled cool-down, then depowdering and bead blasting. Days, not hours.
- Colour. Natural PA12 is off-white and porous; parts are usually dyed black.
Side by side
| FDM | SLA | SLS | |
|---|---|---|---|
| Detail | Moderate | Excellent | Good |
| Surface finish | Layer lines | Smooth, moulded look | Matte, slightly grainy |
| Strength | Good, weaker in Z | Low to moderate, brittle | Excellent, near-isotropic |
| Typical tolerance | ±0.3 mm | ±0.1 mm | ±0.3 mm |
| Supports needed | Yes | Yes | No |
| Cost for one part | Lowest | Moderate | Highest |
| Cost for fifty parts | Moderate | Moderate | Lowest per unit |
| Best automotive use | Housings, jigs, prototypes | Emblems, bezels, detail trim | Clips, hinges, load-bearing trim |
Numbers are planning figures, not guarantees. For a real tolerance answer on a real part, see 3D printing tolerances: what to expect on automotive parts.
Choosing in practice
Ask four questions in this order:
- Does it carry load or get flexed? If yes, SLS nylon first, FDM second. Not resin.
- Does anyone look at it up close? If yes, SLA — or FDM with a proper paint process.
- How hot does it get? A part on a dashboard behind glass can pass 70 °C in a Slovenian summer. PLA and standard resin both give up. ASA, PA12 and polycarbonate do not.
- How many do you need, and when? One part tomorrow is FDM. Eighty parts next week is SLS.
The short version
- Cheap, big and functional → FDM
- Detailed and good-looking → SLA
- Strong, complex and production-ready → SLS
Still not sure? That's what the file review is for — send the part and the use case and we'll tell you which process we'd run and why. Read more about our 3D printing service, or, if the part exists but the CAD doesn't, about 3D scanning.
Planning a production run rather than a one-off? The break-even maths is in SLS nylon vs injection molding, and larger programmes go through our enterprise service.
The Mercedes R129 roofelight cover shown with this article is one we print in PETG on the FDM line — a straightforward trim piece, the kind of part where FDM's speed and cost beat SLA or SLS without giving anything up.
SHIPS 3–5 DAYS
