Home / SLA vs SLS Guide
Guide for design and manufacturing engineersSLA or SLS: pick the process before you ask for the quote.
SLA vs SLS is the first decision on any printed part, and it sets the material list, the surface, the tolerance and the price at volume. This guide makes the comparison the way we make it at the quote: by what the part has to do, not by which printer is free.
SLA vs SLS comes down to four questions: what the finest feature is, what the surface has to look like, what load the part takes in service, and how many you need. Stereolithography on the Form 4B cures liquid resin with a laser and wins on detail, finish, clarity and biocompatible work. Selective laser sintering on the Formlabs Fuse fuses nylon powder and wins on toughness, support-free geometry and the price of a short run. Both are the same shop, the same design review and the same scan verification, so the recommendation is about the part, not about which machine we would rather run.
The pages for each process go deeper: SLA 3D printing for the resin families and the biocompatible work, SLS 3D printing for the powders and repeat runs, and the materials page for every family with its data sheet.
Decision table
Ten criteria, side by side.
General figures for most parts, not a promise for yours. Read the row that matters most to your part first; that row usually decides the process.
| Criterion | SLA, Form 4B | SLS, Formlabs Fuse |
|---|---|---|
| Feature detail | Sharpest. Threads, engraved text, thin walls and small holes at layers down to 25 microns. | Good, not fine. Small features soften and holes under about 1 mm tend to close. |
| Surface finish | Smooth, close to a moulded finish; paintable and platable. | Matte and slightly grainy, uniform on every face; can be blasted, dyed or sealed. |
| Strength and isotropy | Depends on the resin; layer direction matters on some. Tough and Rigid families cover most loads. | Nylon 12 is tough and near isotropic; the default for parts that go into service. |
| Flexible parts | Elastomeric and silicone resins for gaskets, grips and boots. | TPU 90A for ducting, bellows and covers, with no supports to trim. |
| Clear parts | Yes. Clear resins, polishable to near optical clarity. | No. Nylon is opaque. |
| Biocompatible | Yes. BioMed resins on the Form 4B, with the documentation Formlabs publishes. | Not offered as a biocompatible process here. |
| Support marks | Yes, on the supported faces; placed on non-critical faces at design review. | None. The unfused powder holds the part. |
| Cost per part, 1 to 10 parts | Usually lower for small parts; a single part is a single build. | Usually higher; the build costs about the same whether it holds one part or forty. |
| Cost per part, 50 to 500 parts | Rises with quantity; each part needs its own platform area and post-processing. | Usually lower; parts nest in three dimensions inside one build. |
| Typical lead time | Prototypes typically 3 to 5 working days. | Prototypes typically 3 to 5 working days; a full batch nests in one build. |
Routing
If the part must...
Choose SLA when the part must
- Hold a thread, engraved text or a wall under 1 mm
- Look and feel like the moulded part, straight off the printer
- Be clear enough to show flow, fill or an internal channel
- Contact skin or tissue on a biocompatible resin
- Sit near heat or take short autoclave cycles
- Serve as a pattern or master for casting or moulding
Choose SLS when the part must
- Go into service and survive handling, drops and assembly
- Flex as a living hinge or click as a snap fit, cycle after cycle
- Print as one piece: interlocking, hollow or with internal channels, with no supports
- Replace a metal bracket with stiffness and low weight, in Nylon 11 CF
- Bend, seal or cushion as a flexible TPU part
- Run as a batch of 50 to 500 at a sensible price per part
3D printing tolerances
What each process typically holds.
Typical figures for SLA and SLS tolerances on well designed parts, by feature size. They are a starting point for design, not a specification.
| Feature | SLA, typical | SLS, typical |
|---|---|---|
| Small features, under 25 mm | Typically within ±0.1 mm for most parts | Typically within ±0.3 mm for most parts |
| Medium features, 25 to 100 mm | Typically ±0.1 to ±0.2 mm | Typically ±0.3 mm, or about ±0.3% on the longer dimensions |
| Large features, over 100 mm | Typically about ±0.2% of the dimension | Typically about ±0.3% of the dimension |
| Minimum wall | Typically 0.5 mm when supported; 1 mm for a wall that has to survive handling | Typically 0.7 to 1.0 mm |
| Minimum hole | Typically 0.5 mm | Typically 1.0 to 1.5 mm, so trapped powder can be cleared |
| Text and embossing | Typically 0.3 mm line width and height | Typically 0.5 mm line width and 1 mm height for legibility |
The achievable tolerance depends on the geometry, the orientation on the build platform and the material. CETS confirms the tolerance for your part on the quote, and verifies the critical dimensions on the finished part by scan on the MetroY Ultra, with a written record.
How scan verification worksEngineering first
One shop designs it, checks it and makes it.
- Design review before anything prints: material, orientation, tolerances and how the part will fail.
- Scan verification after: the finished part measured against the model on the MetroY Ultra, with a written record.
- A drawing and the CAD you own, so the next order is a reorder, not a second engineering job.
- Design and build, or reverse engineer and build, under one roof, in Puerto Rico and for the US mainland.
CETS serves Puerto Rico and the US mainland, with international service available.
FAQ
Common questions
Is SLA or SLS more accurate?
SLA typically holds the tighter tolerance and the finer feature, because a laser cures liquid resin at layers down to 25 microns. SLS holds a looser tolerance but with no support marks and near isotropic strength. For most parts the choice is decided by which feature matters, and we confirm the achievable tolerance for your geometry on the quote.
Which is cheaper, SLA or SLS?
For one to ten small parts SLA is usually cheaper. From about fifty parts upward SLS is usually cheaper, because parts nest in three dimensions inside one build and share its cost. If the volume is uncertain, ask for both figures on the quote.
Can one assembly use both processes?
Yes, and it is common: a clear SLA window or a biocompatible SLA contact part inside a Nylon 12 SLS housing. Each part is quoted in its own process, and the fit is checked before the assembly ships.
Are the tolerances in the table guaranteed?
No. The table gives typical industry figures for reference. The tolerance CETS commits to is the one written on your quote, for your geometry, orientation and material, and it is verified by scan on the finished part with a written record.
Related pages
Still not sure? Send the part and we decide it with you.
A CAD file, a drawing or a photo is enough. The written quote arrives in one business day and names the process, the material and the tolerance we will hold.
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