What is SLA 3D printing and what is it best for?

SLA — stereolithography — builds a part by curing liquid photopolymer with ultraviolet light, layer by layer, in a vat. It produces the smoothest surface and the finest feature resolution of any widely available additive process, which makes it the right call for cosmetic prototypes, presentation and sales models, master patterns for silicone moulding and investment casting, dental and jewellery work, and any part carrying fine text, thin walls or sharp edges. It is the wrong call for load-bearing parts that must survive months of service, for anything living outdoors in sunlight, and for large structural components where FDM or SLS will be cheaper and tougher.

How much do SLA 3D printing services cost?

SLA quotes are driven by part volume and resin grade far more than by machine time, because the vat is charged for what it consumes and speciality photopolymers cost several times what standard grey does. The levers that actually move the number are the bounding volume of the part, whether it is hollowed with drain holes, the resin family you specify, and finishing labour — support-nub removal, sanding and clear-coating on a cosmetic face is often the largest single line on the invoice. Ask for the quote split into resin, machine time and finishing, and ask specifically what finish level the price assumes.

How accurate is SLA, and what tolerances can a bureau hold?

SLA is among the most dimensionally precise plastic additive processes, and bureaus commonly quote in the region of ±0.1–0.2 mm on small parts or around ±0.2% on larger ones, with feature resolution down to a few tenths of a millimetre. The caveat is that photopolymer keeps moving after it leaves the machine: post-cure shrinkage and slow ageing mean a part measured on the day it ships is not guaranteed to measure the same in six months. If you are checking a fit, check it early, and tell the provider which dimensions are critical so they can orient and compensate for them.

What is the difference between SLA, MSLA and DLP?

All three cure liquid photopolymer with UV light and all three produce the smooth, high-detail parts resin is known for; they differ only in how a layer is exposed. Traditional SLA traces each layer with a laser spot. DLP projects the whole layer at once with a digital micromirror device. MSLA — masked SLA — flashes an LCD panel, which is what nearly every desktop machine uses. Layer exposure time is independent of how many parts are on the plate for DLP and MSLA, so they are faster on full builds; laser SLA tends to scale better to large format. For most buyers the ordered part is comparable, so specify accuracy and finish rather than the mechanism.

Are SLA parts strong enough for functional use?

Standard photopolymer is not a functional material — it is stiff, notch-sensitive and snaps rather than bends, and it embrittles further with UV exposure and time. Engineering photopolymers change the picture considerably: tough and durable grades approximate ABS or polypropylene behaviour, and high-temperature grades hold shape well above where standard resin sags. They still age faster than a thermoplastic. Use SLA for short-life functional prototypes and for fit and appearance work, and move to SLS nylon or an FDM engineering plastic when the part has to keep working for months under load.

Should I use an SLA service bureau or buy a desktop resin machine?

Use a bureau for large parts, speciality and biocompatible resins, certified or documented work, and anything printed infrequently — the messy part of resin is not the printing, it is the washing, curing, waste handling and ventilation, and that overhead does not shrink for occasional use. A desktop machine earns its place when you print small detail parts often enough to keep it busy and have a ventilated space to dedicate to it. Plenty of teams run both: desktop iterations during design, and a bureau for the final cosmetic parts and anything needing a resin they do not stock.

SLA 3D Printing Services — How to Spec and Order Detail Parts

SLA 3D printing services exist for the jobs where the surface is the point. When a part has to photograph well, drop into a sales meeting, carry legible 1 mm text, or serve as the master for a silicone mould, stereolithography is the process that gets you there without a finishing bill that dwarfs the part. It is also the process most often ordered as though it were a thermoplastic — and photopolymer is not a thermoplastic, which is where most disappointments come from. This guide covers what SLA is genuinely good at, what actually drives your quote, how to spec a part so the shop can hit it, and how to tell a capable bureau from a cheap one. Browse 3D printing providers when you are ready to send the job out.

What SLA Actually Is, and When It Is the Right Call

SLA — stereolithography — cures liquid photopolymer with ultraviolet light, one layer at a time, in a vat. Because a light source can be focused far more tightly than molten plastic can be extruded, the process resolves features an extruder cannot approach, and the surface comes off the machine essentially smooth. Everything good and bad about SLA follows from that one mechanism.

SLA is the right call for:

Cosmetic prototypes and appearance models where layer lines would kill the illusion
Master patterns for silicone moulding and urethane casting, where every flaw in the master is copied into every part
Castable patterns for jewellery and investment casting, which burn out cleanly
Dental models, surgical guides and aligner work, where biocompatible grades and fine detail are both mandatory
Small assemblies with thin walls, sharp edges, fine text or textured surfaces
Fit-check parts where you need the tightest dimensional agreement with the CAD you can get in plastic

SLA is the wrong call when the part has to survive. Standard photopolymer is stiff and brittle, it yellows and embrittles under UV, and it keeps ageing on the shelf. A bracket that passes its test on Friday can be noticeably more fragile a few months later. If the part carries load for a working life, SLS nylon or an FDM engineering plastic is the honest answer, and it is usually cheaper too.

The Thing Most Buyers Get Wrong: Resin Choice Is an Engineering Decision

Most SLA quotes are returned in the shop's default standard grey unless you say otherwise, and standard grey is a visual material — it exists to look good and hold detail. Buyers who ask for "SLA" and get a part that shatters in a drawer usually specified the process and left the material to chance.

Resin family	What it is for	What it costs you
Standard	Appearance models, master patterns, visual prototypes	Brittle, poor impact resistance, ages under UV
Tough / durable	Snap fits, short-life functional prototypes, housings	30–80% material premium, slightly softer detail
High-temperature	Parts near heat, mould inserts, thermal fixtures	Usually more brittle again; often needs a longer post-cure
Castable	Investment-casting and jewellery patterns	Fragile to handle; sized for burnout, not for service
Biocompatible / dental	Guides, splints, models in a clinical workflow	Certified supply chain, documented cure cycle, higher price
Flexible / elastomeric	Gaskets, grips, soft-touch prototypes	Limited stock at smaller shops; slower to print

Tell the provider the operating environment rather than the resin name. "It lives in a car cabin in Arizona" or "it gets handled by a customer at a trade show for two days" gets you a better recommendation than a grade you found in a spec sheet, and it lets the shop tell you when SLA is not the right process at all.

How SLA Pricing Actually Works

SLA prices on volume, not on footprint. The vat is consumed by what the part displaces, plus the support lattice, plus the raft — so geometry that a buyer thinks of as "small" can be expensive if it is solid.

The levers, roughly in order of how much they move the number:

Part volume. Hollowing a solid model and adding drain holes can cut the resin in a large part dramatically. Ask whether hollowing is acceptable for your application before you assume it is not.
Resin grade. Speciality photopolymers run several times the cost of standard, and biocompatible grades carry documentation overhead on top.
Finishing level. This is the line buyers underestimate most. Support nubs on a cosmetic face have to be sanded and blended by hand, and a painted or clear-coated finish is skilled labour. A "raw, as-printed, supports removed" price and a "presentation finish" price for the same geometry are not close to each other.
Machine time and layer height. Finer layers mean more exposures. Dropping from 100 µm to 25 µm can quadruple the build.
Turnaround. Rush work displaces other jobs on the plate, and rush surcharges on resin work are common because the post-cure cycle cannot be shortened safely.

Ask for the quote broken into resin, machine time and finishing. If a shop will not split it, you cannot tell which lever to pull, and you will end up negotiating the only number you can see.

How to Spec and Order an SLA Part

Send solid, watertight geometry. STL is standard for SLA; STEP is better when tolerances matter, because it preserves the true surfaces rather than a triangulated approximation. Which format to send and why changes what the shop can verify before printing.
Name the cosmetic faces. Supports have to touch the part somewhere. If you do not say which surfaces must be flawless, the shop chooses for you — usually the orientation that prints fastest.
Call out the critical dimensions. A drawing with three toleranced features is far more useful than a blanket tolerance across the model, and it lets the shop orient and compensate deliberately. Our guide to tolerances and accuracy covers what is reasonable to ask for.
Specify the finish in words, not adjectives. "Supports removed, nubs sanded flush, no paint" is a specification. "Nice finish" is a dispute waiting to happen.
State the post-cure expectation. Under-cured parts are weaker, tackier and dimensionally unstable; over-cured parts are more brittle. A shop that has a documented cure cycle per resin is telling you something useful about the rest of its process. The same variables show up on the desktop — see resin safety and post-processing basics.
Say when you will measure it. If the part is going on a CMM, measure it soon after delivery and agree that with the provider, because photopolymer does not hold still indefinitely.

What to Look For in an SLA Provider

Ask which machine class your part will run on. Large-format laser SLA, production DLP and desktop MSLA are all sold as "SLA", and the difference shows up in build volume, plate-to-plate consistency and what happens when you order the same part again in three months.

Then ask four questions:

Which resins do you stock, and which do you order in? A shop that stocks one standard grey and buys everything else in has a longer lead time than its quote implies.
What is your post-cure procedure for this resin? You want a time and a temperature, not "we cure everything".
Who removes the supports, and to what standard? The answer tells you whether finishing is a process or an afterthought.
Can you reproduce this part later? Batch-to-batch consistency on photopolymer depends on resin lot, vat age and cure discipline. If this is a master pattern you will re-cut, it matters.

If the shop is also quoting your post-processing and finishing in-house rather than subcontracting it, you generally get a shorter loop and a single point of accountability when a cosmetic part comes back wrong.

Related Processes Worth Comparing

Process	Choose it over SLA when
FDM	The part is large, structural, or needs a real thermoplastic — and cost matters more than finish
SLS	You need durable, support-free nylon parts with complex geometry and a working life
PolyJet	You need multi-material, multi-colour or over-moulded soft-touch features in one build
Urethane casting	You need 10–100 copies of an SLA-quality part in a production-like material

The two head-to-head comparisons buyers ask for most are SLA vs FDM and SLA vs SLS. If multi-material is on the table, PolyJet services cover ground SLA cannot. And if you are sourcing in the Southeast specifically, we have a regional page for SLA services in Georgia.

Find an SLA Provider

SLA is widely available — almost every plastics bureau runs resin of some kind — so the real sourcing question is not who owns a machine but who runs the finishing and cure discipline that makes resin parts worth ordering. Send the same geometry, the same resin family and the same written finish spec to two or three shops and compare what comes back, including how they answer the four questions above.

Browse verified 3D printing providers in the directory and filter by technology — and if the part is cosmetic and fragile, weigh a shop close enough to collect from by hand over one that has to trust it to a courier.

Hero photograph by EnCata PD.