SLA 3D Printing: How It Works, Key Specs, Materials, Pros/Cons, Applications

SLA (stereolithography) is a laser‑based vat photopolymerization process that builds parts layer by layer from liquid resin. It delivers crisp detail, smooth surfaces, and reliable accuracy—ideal for visual prototypes and precision components. Wondering when to pick SLA over other processes? Choose it when fine features, clarity, or tight cosmetics matter more than raw toughness.

Key takeaways

SLA uses a focused UV laser to selectively cure resin; orientation and supports strongly influence quality.
Key specs include layer height, laser spot size (XY resolution), and post‑cure parameters.
Strength and durability hinge on resin choice and post‑processing; many resins are more brittle than thermoplastics.
Applications include clear optics, dental/medical models (with certified resins), jewelry masters, and microfluidics.

How SLA works and key technical points

Workflow: prepare CAD, orient the part, generate supports, slice; the laser scans each layer, the platform lifts, resin recoats, and the cycle repeats. After printing, parts are washed to remove uncured resin, dried, UV post‑cured, supports removed, and surfaces finished. Orientation balances accuracy, support scars, and print time; hollowing thick sections and keeping wall thicknesses consistent help reduce stress. Supports are mandatory for overhangs and long flats; placing them on non‑critical faces preserves cosmetics. Resolution depends on laser spot size and layer height; thinner layers and smaller spot sizes capture finer detail but add time. For pragmatic DFM tips on tolerances, wall thicknesses, and clearances, see Xometry’s SLA design guidelines (2025).

Pros and cons in practice

Pros: SLA delivers crisp detail, smooth sidewalls, and dependable accuracy without tooling. It captures fine text and micro‑features, supports thin walls and watertight channels, and—with polishing—can produce optically clear parts for show‑quality prototypes and precise patterns. Surface finish is superior out of the printer, small internal passages are feasible, and dimensional repeatability across batches is strong when parts are oriented consistently. It’s well suited to cosmetic prototypes, masters for casting, and tight‑tolerance visual components.

Cons: Wash, dry, UV cure, and support cleanup add time and handling. Support contact leaves marks needing sanding; orientation influences success, cycle time, and where scars appear. Many resins are brittle, UV‑sensitive, and heat‑limited (lower HDT), so rugged snap‑fits, outdoor exposure, or high‑temperature use often require specialty grades or another process. Parts can yellow over time, large flat areas may warp without careful design, and uncured resin demands PPE and good ventilation during post‑processing.

SLA resin materials

Material families cover most prototyping needs, but properties vary widely by formulation. Selection is a balance of clarity vs toughness, HDT vs brittleness, and chemical/UV resistance vs ease of finishing. Post‑cure greatly affects final strength, heat resistance, and dimensional stability; pigments and fillers can change viscosity, printability, and polishability. For regulated uses, match the exact printer/resin/post‑cure workflow validated by the manufacturer.

Material family	Typical uses	Strengths	Trade‑offs / cautions	Notes
Standard & clear	Visual models, lenses/light pipes, transparent housings	Near‑optical clarity after polishing; smooth surfaces	May yellow under UV; lower toughness than thermoplastics	Best for cosmetic prototypes; handle UV exposure carefully
Tough / durable	Impact‑resistant prototypes, snap‑fits, functional covers	Better elongation and toughness; improved impact resistance	Some loss of ultimate stiffness; properties vary by grade	Validate fit for snap‑features; orient consistently for repeatability
Rigid / ceramic‑filled	Fixtures, jigs, dimensionally stable components	High stiffness and creep resistance; good dimensional stability	Lower impact strength; abrasive to finishing tools	Use sharp abrasives; expect more brittle behavior
High‑temperature	Short‑run tooling, thermal test fixtures, mold inserts	Higher HDT after full post‑cure; brief elevated‑temperature exposure	Can be brittle; requires precise post‑cure for performance	Follow resin‑specific cure schedules for heat resistance
Flexible / elastic	Soft‑touch parts, seals, form‑fit testing	Elastic response; compressibility for sealing	Risk of tearing if features are too thin; limited long‑term durability	Respect minimum wall/feature sizes; consider support placement
Dental / medical (certified)	Surgical guides, dental models, appliances	Biocompatible grades validated for specific workflows	Use only within validated sterilization and biocompatibility protocols	Match exact printer/resin/post‑cure per manufacturer guidance
Castable (investment casting)	Jewelry masters, small metal part patterns	Clean burnout with proper cycles; fine feature capture	Requires controlled burnout and careful pattern handling	Coordinate foundry schedules; minimize ash residues
ESD / flame‑retardant	Housings and fixtures needing electrostatic control or UL‑style ratings	Functional properties (ESD control, FR behavior)	Typically reduced surface clarity and more challenging finishing	Confirm rating requirements; prioritize function over cosmetics

Applications and SLA vs FDM

SLA fits precision visual prototypes, optical/clear components, jewelry masters and casting patterns, microfluidic devices, and medical/dental models where the resin’s certifications apply. It’s also useful for short‑run fixtures and patterns when surface quality is paramount. Engineers also leverage SLA for watertight fluid manifolds, light pipes and lenses, ergonomic mockups with crisp cosmetics, and high‑detail master patterns for silicone molding or investment casting. With proper post‑cure and finishing, it can serve as a surrogate for limited functional testing where fine channels, smooth seals, or transparency are critical.

Compared with FDM, SLA typically delivers finer detail and a smoother finish, while FDM often wins on durability for rugged fixtures and cost on larger parts. SLA excels when you need small minimum feature sizes, tight tolerances on fine details, smooth internal passages, or biocompatible/medical‑workflow resins. FDM is preferable for high‑temperature plastics, impact‑resistant tooling, large build volumes, and parts that will live outdoors. Consider build size limits, isotropy requirements, watertightness, and post‑processing: SLA offers excellent cosmetics but needs support cleanup; FDM lines are visible but supports can be easier to remove on some geometries. Hybrid workflows are common—print an SLA master for appearance, then duplicate via molding, while using FDM for jigs, nests, or protective brackets.

Post‑processing and safety

Performance depends on correct washing, full drying, and UV post‑cure cycles recommended by the resin maker. Surface quality can be elevated with sanding, polishing, and coatings; see this guide to surface finishing methods. Handle uncured resin with gloves, eye protection, and ventilation; always follow the resin’s SDS for disposal and safety.

When to work with a service provider

If you need validated tolerances, material guidance, or production‑like finishing, a professional service can help. Kaierwo supports SLA alongside other processes and can assist with resin selection and finishing planning. Disclosure: Kaierwo is our product. For efficient quotes, provide native CAD, key dimensions/tolerances, resin preferences, cosmetic requirements, quantity, and target timeline.

References and standards

For formal definitions, see the ISO/ASTM 52900 vocabulary in ISO/ASTM 52900:2021 terminology. For material selection beyond the Stratasys and Xometry resources cited above, compare resin properties and trade‑offs in the Fictiv SLA materials guide. For deeper technical background on mechanisms, properties, and applications, this peer‑reviewed overview provides helpful context: 2020 vat photopolymerization review (Polymers, open access via PMC). These references help align terminology, validate data, and support engineering decisions.