Choose FDM for low-cost prototypes, jigs and larger simple parts; SLA (and the DLP and MSLA resin family) for fine detail, smooth surfaces and small precise parts; and SLS for tough nylon parts with complex shapes, especially in batches. Each process wins on a different mix of tolerance, finish, strength, cost and lead time, and the right choice depends on what the part has to do, how many you need and how soon.
Key points
- FDM is the cheapest and fastest route for one-offs and large, simple parts, but shows layer lines and is weaker between layers.
- SLA gives the smoothest surface and finest detail; standard resins are brittle and every part needs washing, curing and support removal.
- SLS makes tough, nearly isotropic nylon parts with no supports, and is most economical when parts share a build.
- Tolerances are tighter for resin than for SLS, and for SLS than for typical FDM, but all depend on part size.
- Lead time follows the process: FDM and resin can turn around quickly; SLS waits for builds to fill and cool.
How do the three processes work?
- FDM melts a plastic filament and lays it down line by line. Overhangs need support structures that are removed afterwards.
- SLA cures liquid resin with light, layer by layer; laser SLA traces each layer, while DLP and MSLA expose each layer at once. Parts need supports, then washing and UV curing.
- SLS fuses nylon powder with a laser. The surrounding powder supports the part, so no supports are needed and parts can be stacked in three dimensions.
How do FDM, SLA and SLS compare?
The figures below are typical ranges for professional equipment and service suppliers. Your machines and materials will differ; treat them as a starting point and ask the supplier for theirs.
| FDM | SLA, DLP, MSLA | SLS | |
|---|---|---|---|
| Typical tolerance | Often ±0.2-0.5 mm | Often ±0.1-0.2 mm on small parts | Often ±0.3 mm, or about ±0.3 % on larger parts |
| Typical layer height | 0.1-0.3 mm | 0.025-0.1 mm | Around 0.1 mm |
| Surface finish | Visible layer lines | Smooth, fine detail | Matte, slightly grainy |
| Strength | Good in-plane, weaker between layers | Stiff; standard resins brittle, tough grades available | Tough, close to uniform in all directions |
| Supports | Needed for overhangs | Always needed | None |
| Materials | PLA, PETG, ABS, ASA, TPU, PC, nylon and fibre-filled grades | Standard, tough, flexible, high-temperature, castable and dental resins | PA12, PA11, filled nylons, TPU, PP |
| Cost for one part | Lowest | Low to moderate; labour-heavy | High unless it shares a build |
| Cost in batches | Scales with machine count | Good when plates are full | Often lowest for small parts |
| Typical lead time | Same day to a few days | One to a few days | Several days, set by builds and cooling |
| Typical parts | Prototypes, jigs, fixtures, enclosures, large simple parts | Miniatures, dental, jewellery patterns, small precise parts, cosmetic models | Functional prototypes, housings, clips, snap fits, low-volume production |
Which process gives the best tolerance and finish?
Resin gives the finest features and the smoothest surface straight off the machine, which is why it is the default for dental models, jewellery patterns and cosmetic prototypes. Its accuracy is best on small parts; large flat resin parts can warp as they cure.
SLS parts have a uniform matte texture with no layer lines visible at arm’s length and no support marks. They can be dyed, blasted or vapour smoothed. FDM parts show layer lines and, where supports touched, rougher patches, though orientation and finishing reduce both. Our guide to surface finish options covers what each finish costs, and tolerances and cost explains why tighter limits always cost more.
If you need a measure, surface roughness values vary widely with orientation and settings on all three, so compare samples from your supplier rather than generic numbers.
Which process gives the strongest parts?
Strength depends as much on material as on process, but each process has a character.
- FDM parts are strong along the deposited lines and weaker across layers, a clear case of anisotropy. Orient the part so the main load runs along the layers.
- Resin parts are stiff and accurate, but standard resins are brittle. Tough, durable and high-temperature resins exist; they cost more per litre.
- SLS nylon is tough, resists fatigue and impact well and behaves similarly in all directions. It is the usual choice for snap fits, living hinges in short runs and parts that take repeated load.
How do costs compare?
The cost structure differs more than the price per gram. FDM cost is mostly machine time, so it scales with print time per part. Resin cost on small parts is mostly labour: washing, curing and removing supports for each part, as worked through in resin printing cost. SLS cost is a share of a whole build, so a single part on its own is expensive and a batch of small parts is cheap, as set out in SLS pricing and nesting.
That leads to a simple rule of thumb:
| Order | Usually cheapest | Why |
|---|---|---|
| One large, simple part | FDM | No shared build, little post-processing |
| One small, detailed part | Resin, if it can share a plate | Machine time is shared; labour per part is small for one piece |
| 10-100 small functional parts | SLS or MJF | The build is shared, parts stack in 3D, no supports to remove |
| Hundreds of identical parts | SLS or MJF, or moulding | Above some quantity, tooling starts to pay; see 3D printing vs injection moulding |
For the line-by-line method behind any of these prices, see how to calculate 3D printing cost.
How do lead times compare?
FDM and resin jobs can start as soon as a machine is free, so a shop with spare capacity can turn them in a day. SLS shops usually batch work into builds, which means waiting for a build to fill, then printing, then a cool-down that can last about as long as the print. Several working days is common. A dedicated SLS build can shorten that, at the cost of carrying the whole build.
Where do MJF and other processes fit?
MJF sits next to SLS: the same nylon materials, the same support-free freedom and the same build-share pricing, usually with grey or black parts and often a lower cost per part in production quantities. For most of the comparisons on this page, read “SLS” as “SLS or MJF”.
Beyond these, PolyJet gives full-colour and multi-material models with a smooth finish but weaker parts, and metal powder-bed fusion makes dense metal parts at a much higher cost, covered in what drives the cost of metal 3D printing. If the part is a simple shape in a production quantity, machining or moulding may beat all of them.
Common mistakes when choosing a process
- Choosing by the surface of a photo. A beautiful resin print may be too brittle for a clip; a matte SLS part may be fine once it is dyed.
- Ignoring orientation. FDM strength, resin support marks and SLS build share all change with how the part sits in the machine.
- Comparing a single-part price only. SLS looks expensive for one part and cheap for fifty. Ask for prices at the quantity you will really order.
- Forgetting the finish. A raw FDM part plus an hour of sanding may cost more than an SLS part dyed as standard.
How to choose, part by part
- Does it need fine detail or a smooth surface without finishing? Resin.
- Does it need toughness, snap fits or complex internal shapes with no supports? SLS, or MJF; see MJF vs SLS for the difference.
- Is it large, simple, or needed today at the lowest cost? FDM.
- Is it a batch of small functional parts? SLS or MJF.
- Does it need a specific material? Start from the material and see which processes offer it.
Whichever you choose, design to that process’s rules on walls, holes and overhangs. Our design for 3D printing guide covers them.
Quotometry prices FDM, SLA/DLP/LCD resin, SLS and MJF (and metal, PolyJet and binder jetting) from one analysis of the part, so a shop can show a buyer the same part priced in each process side by side. The technologies overview lists each process and how it is priced.
Questions people ask
Which 3D printing process is the most accurate?
Resin (SLA, DLP and MSLA) usually holds the finest detail and the tightest tolerances on small parts, because its layers and spot or pixel size are small. SLS and MJF come next for functional parts. FDM is the least precise in general, though a well-tuned printer does well on simple geometry. For any process, accuracy falls as parts get larger and thicker.
Which 3D printing process gives the strongest parts?
For general functional parts, SLS nylon is tough and behaves similarly in every direction. FDM in engineering filaments such as PETG, ABS, PC or fibre-filled nylon can be very strong along its layers but weaker between them. Standard resins are stiff but brittle, though tough and engineering resins narrow the gap. The load direction and the material matter as much as the process.
Which process is cheapest for one part?
Usually FDM, especially for larger simple parts, because it needs no shared build and little post-processing. A small resin part can be competitive if it can share a plate. A single SLS part is cheap only if it can join a build with other work; on its own it carries most of a build's cost. For batches of small parts, SLS often becomes the cheapest.
Can I switch a design from FDM to SLS without changes?
Often, but check three things. SLS needs no supports, so you can remove features added only to help FDM. Enclosed hollow spaces trap powder in SLS and need escape holes. Thin walls and gaps that worked in FDM may need adjusting to the SLS supplier's minimum wall and clearance rules.
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