What Is SLA 3D Printing? A Formlabs Guide to Stereolithography

What Is Stereolithography (SLA)?

Stereolithography — also called vat photopolymerization or resin 3D printing — is an additive manufacturing process that uses a UV light source to cure liquid photopolymer resin into solid plastic parts, one thin layer at a time. Formlabs has been a leading force in making this technology accessible since it brought the first desktop SLA printer to market in 2013.

How Does SLA 3D Printing Work?

A resin tank holds liquid photopolymer. A precisely controlled light source exposes selected areas of the resin surface, causing it to harden through a process called photopolymerization. The build platform then moves, exposing the next layer, until the full part is complete. Formlabs printers use an inverted, bottom-up approach that keeps the optics clean and enables high repeatability.

Key Advantages of SLA

• Surface finish: SLA produces the smoothest surfaces and finest details of any common 3D printing technology.
• Accuracy: Tight tolerances make parts suitable for multi-component assemblies and functional prototypes.
• Material versatility: A wide library of engineering resins covers general-purpose, high-temperature, flexible, rigid, and specialty applications.
• Isotropy: Parts are watertight and have consistent mechanical properties in all directions.

Post-Processing

After printing, parts must be washed in a solvent to remove uncured resin, supports are removed, and the part is post-cured under UV light to reach full strength and dimensional stability. Skipping or rushing these steps can leave parts tacky or dimensionally inaccurate.

Who Uses SLA and For What?

Engineers, manufacturers, dental professionals, and product designers rely on SLA for rapid prototyping, end-use parts, tooling, manufacturing aids, and investment casting patterns. The broad resin selection — from standard to biocompatible and high-temperature formulations — means SLA scales from desktop experimentation to full production workflows.