What is SLA 3D Printing?

Last updated September 27, 2026

SLA (stereolithography) is a 3D printing process that builds parts from liquid resin. It is the best option on OpusFab when you need fine detail and a smooth surface, and it is commonly used for visual prototypes, fit checks, and presentation models.

How it works

SLA is a vat photopolymerisation process:

  1. A tank (vat) is filled with liquid photopolymer resin, a plastic that hardens when exposed to ultraviolet light.
  2. A build platform sits just below the resin surface.
  3. A UV laser traces the shape of one thin layer of your part onto the resin, curing it solid.
  4. The platform lifts, fresh resin flows over the surface, and the next layer is cured.
  5. After printing, the part is washed to remove uncured resin and post-cured under UV light to reach full strength.

Because parts are built layer by layer, SLA handles complex shapes, sharp details, and internal features that a cutting tool could not reach. Thin-walled or overhanging features are printed with temporary support structures, which are removed after printing.

Surface quality

SLA produces a perfectly smooth surface, the smoothest of the common 3D printing processes and the closest in feel to an injection moulded part. Layer lines are far less visible than with filament (FDM) or powder (SLS) printing, and fine features like small text, logos, and threads come out crisp. On OpusFab, SLA parts are offered in the raw “As Printed” finish only; no other finishes are currently available on printed parts. See Surface finishes overview.

Materials: SLA resins

OpusFab offers three SLA resins:

  • Standard Resin (9400, white): the general-purpose photopolymer, suited to appearance models and light-duty functional parts. This is also the large-format option.
  • Tough Resin (black): stronger and more heat resistant than Standard Resin.
  • Red Wax Resin (castable): for lost wax casting patterns and miniatures.

SLA resins are generally more brittle than machined plastics or metals and can degrade with long UV or heat exposure. For parts that take real mechanical load, consider SLS nylon or CNC machining. Check the quote editor for the current live material list.

Build volume

Standard Resin (9400) prints up to 1700 x 800 x 600 mm, and Tough Resin (black) up to 800 x 600 x 600 mm. Wax parts are typically small. If your part is larger than these volumes, it can be split and bonded, or quoted for CNC machining instead.

Tolerances

The standard tolerance shown at checkout for SLA parts is ±0.5mm. That is looser than CNC machining (±0.05mm), so SLA is not the right process for precision fits between mating parts. For form and fit checks where you mainly need to confirm a part fits inside an enclosure, it is usually good enough. See Tolerances explained.

When to use SLA

SLA is the right call when:

  • You need a visual or concept prototype that looks close to the final product.
  • Surface finish and fine detail matter more than strength.
  • You want a quick form and fit check, such as confirming a part fits with mating components.
  • You are iterating fast on a design that is still changing, since printed parts cost less per iteration than machined ones.

SLA is not the right call for parts under sustained mechanical load, high heat, or outdoor exposure, and not for tight-tolerance assemblies.

SLA vs. SLS

If you need a stronger printed part, SLS builds from nylon powder and produces functional parts without support structures, at the cost of a rougher, grainier surface. For a full side-by-side of every process on the platform, see Choosing a process.