SLA and DLP resin 3D printing: how to choose the right process
Both processes cure liquid photopolymer with light. SLA draws with a laser spot; DLP flashes a whole layer through a digital projector mask. The choice changes XY resolution, build time, surface texture, and how you orient the part. This page compares the two on the numbers that matter, then states which one suits which part.
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SLA and DLP resin 3D printing compared
Typical values for desktop and mid-range industrial machines. Exact numbers depend on the resin and the machine class.
| Factor | SLA | DLP |
|---|---|---|
| Light source | UV laser, one focused spot | LED array through a DMD projector |
| Exposure per layer | Point-by-point laser scan | Whole layer in a single flash |
| XY resolution limit | Set by spot size, often 0.05–0.15 mm | Set by pixel pitch, often 0.035–0.1 mm |
| Layer time vs part count | Grows with cross-section area | Almost flat, one flash per layer |
| Build volume shape | Usually taller and narrower | Usually wider, projector-limited |
| Surface texture | Fine uniform scan lines | Visible pixel grid on curved faces |
| Large flat layers | Slow, laser must trace the area | Fast, entire layer cured at once |
| Best part count | One or a few large parts | Many small parts per build |
| Resin choice | Broadest range, including high-temp | Good range, slightly narrower |
| Typical use | Large single models, functional jigs | Dental, jewelry, small batch parts |
What actually differs between SLA and DLP
SLA and DLP resin 3D printing both start with a vat of photopolymer and a build platform that rises out of it. The difference is how the light reaches the resin. An SLA machine steers a UV laser with a pair of galvanometers. The beam traces the cross-section of the part point by point, and only the traced line is cured.
A DLP machine places a digital micromirror device between the light source and the resin. Each mirror tilts to either send light to the vat or dump it. One exposure cures the entire layer at once, shaped by that mirror pattern.
That single difference drives almost everything else. Laser tracing takes time proportional to the perimeter and area it must cover. A projector flash takes the same time whether the layer is a thin wall or a solid plate.
The trade is resolution and texture. A laser spot can be focused very small and moved continuously, so curves stay smooth. A projector has a fixed pixel grid, so a curve becomes a staircase of pixels. On a 60 mm wide build area with a 1920 pixel projector, each pixel is about 0.03 mm. That is the smallest feature you can resolve.
XY resolution, pixel grid, and the staircase effect
Resolution claims on spec sheets often mix two numbers. XY resolution is the smallest feature the light can draw. Z resolution, or layer thickness, is how finely the platform steps. SLA machines commonly run 0.05–0.1 mm layers; DLP machines run 0.025–0.1 mm.
On a DLP machine, XY resolution is tied to pixel size. A 0.03 mm pixel draws a 0.03 mm feature, but the edge of any angled surface lands on a pixel boundary. That creates a visible stair step. It shows most on shallow curves, small radii, and text engraved into a flat face.
SLA does not have a fixed grid. The laser draws a continuous path, so a curved wall reads as a smooth line. The trade is time: a large solid cross-section takes much longer to trace than to flash.
If your part has fine lettering, small holes under 0.5 mm, or long shallow curves, the grid matters. If your part is mostly flat or prismatic with a few small features, the grid rarely shows.
Anti-aliasing on newer DLP machines softens the stair step by varying the exposure of edge pixels. It helps on visual models. It does not change the true feature limit.
Build time, part count, and why DLP wins on small batches
Build time is where the two processes separate most clearly. On an SLA machine, layer time depends on how much area the laser must trace. A build with a small cross-section might take 8 seconds per layer. A solid plate covering the same platform might take 40 seconds or more.
On a DLP machine, layer time is close to constant. The projector flashes the whole layer regardless of how full it is. A dense build plate of 40 small parts costs nearly the same time per layer as one part.
That makes DLP the better choice when you need many identical small parts in one run. Dental models, jewelry patterns, and small connector housings fit this pattern. You fill the plate and accept the pixel grid.
SLA wins when the part is large and mostly hollow or shelled. The laser only traces the walls, so a 300 mm tall hollow model builds in reasonable time. Fill the same volume with solid resin and both processes slow down, but SLA slows more.
One more factor: peel force. Every layer the platform must separate from the film. Tall dense parts create more suction, and that sets a floor on layer time in both processes.
Surface finish, dimensional accuracy, and post-processing
SLA surfaces show fine scan lines that run in the laser path direction. They are uniform and shallow, usually easy to sand or bead blast away. DLP surfaces show a pixel grid, which can read as a faint checkerboard under raking light.
Dimensional accuracy depends more on the machine and resin than on the light source. Both processes shrink during cure, and both need compensation built into the file. Shrinkage for common resins runs roughly 0.5–3 percent, and it is anisotropic on some materials.
Support marks are a shared problem. Removing supports leaves witness marks that must be sanded. Place supports on hidden faces when you can, and orient so that visible surfaces do not touch the platform.
Post-processing is nearly identical: wash in isopropyl alcohol, remove supports, post-cure under UV, then finish. Post-cure matters more than most people expect. An under-cured part stays soft and drifts dimensionally over days.
For parts that must hold ±0.05 mm over a long span, neither resin process is the right answer. That is where we move the job to CNC machining, where we hold ±0.005 mm on metal and engineering plastics.
When you should not use either resin process
Resin parts are photopolymers. They are not the same as ABS, polycarbonate, or POM. They creep under sustained load, they lose strength when warm, and they get brittle as they age under UV light. Standard resins soften well below 80 °C.
If the part will sit in an engine bay, carry a structural load, or thread into metal, do not use SLA and DLP resin 3D printing for the final part. Use them for the form check, then machine the real part.
Threaded features are a specific trap. A printed M6 thread in standard resin strips at low torque. Design a clearance hole instead, or print the boss and cut the thread later on a mill.
We often run a hybrid path. Print the housing in resin to confirm fit and connector placement, then cut the production version from 6061-T6 or POM. The printed part costs less and arrives sooner; the machined part holds tolerance and takes load.
If you need an actual engineering plastic in a printed form, that is a different conversation. Our custom 3D printing service covers materials beyond standard resin.
Orientation and support rules that apply to both
Orientation decides more about the final part than the light source does. Tilt the part 10–20 degrees off the platform. A flat face laid parallel to the film creates a large peel area and a suction cup effect that distorts the first layers.
Put supports on the least visible face. Support tips leave small craters, and sanding them flush on a cosmetic surface is slow work. On a functional bracket, hide them inside a pocket.
Drain the part before you cure it. Hollow models need two or more drain holes at low points, at least 2 mm across, or trapped resin will keep curing inside and crack the shell weeks later.
Thin walls under 0.6 mm warp easily in both processes. If the design calls for a thin shell, thicken it to 0.8–1.0 mm in the print file and note the change for the production version.
Keep in mind that the printed part is a check, not the final geometry. When the design is frozen, we cut it from metal and hold the tolerances the resin part could only approximate.
A five-step way to pick between SLA and DLP
Work down the list and stop at the first line that matches your part.
- 1Check the feature sizeIf the smallest feature is under 0.3 mm, or you need readable text under 2 mm tall, lean SLA. The laser spot beats a fixed pixel grid on small detail.
- 2Count the partsMore than about 10 small identical parts per build favors DLP. Layer time stays flat, so the plate fills without adding hours.
- 3Measure the largest cross-sectionA large solid or nearly solid layer favors DLP. A large hollow shell with thin walls favors SLA, because the laser only traces the walls.
- 4Look at the visible facesIf a curved cosmetic face will be seen under raking light, SLA gives a smoother result. If the faces are flat, the pixel grid will not show.
- 5Check the service conditionsAbove 60 °C, sustained load, or UV exposure means neither process. Move the part to CNC machining in aluminum or engineering plastic.
Which process to pick
Pick DLP when you need many small identical parts per build or large flat layers cured fast. Pick SLA when you need fine features, small text, or smooth curved surfaces. If the part must hold ±0.005 mm, carry load, or run above 60 °C, pick neither and machine it from aluminum or engineering plastic instead.
SLA and DLP resin 3D printing questions
Can SLA and DLP use the same resin?
Most 405 nm resins work in both machine types, because both light sources sit in the same UV-A band.
The exposure settings differ, so a resin profile tuned for a laser will over- or under-cure under a projector. Use the profile the resin supplier lists for your machine class.
Which process gives better dimensional accuracy?
Neither wins outright. Accuracy depends on the machine, the resin shrinkage, and how well the file is compensated.
Both processes land in the range of ±0.1 mm on a 100 mm part with a well-tuned profile. Below that, post-cure drift and support removal dominate the error.
Is DLP always faster than SLA?
No. DLP is faster when the cross-section is large or the plate is full, because layer time stays flat.
On a tall, thin part with a tiny cross-section, laser tracing is already fast per layer, and the gap narrows to almost nothing.
Can resin parts be used for functional testing?
For fit checks, light snap fits, and airflow work, yes. For load-bearing or hot-environment testing, no.
Standard resin creeps under sustained load and softens below 80 °C. Use the printed part to confirm geometry, then test the machined version.
How do I get rid of pixel lines on a DLP part?
Sand the surface progressively, or bead blast it for a uniform matte look. A thin primer coat also hides the grid on visual models.
If the part needs a smooth curved face without sanding, reorient it or switch the job to SLA.
What comes after the prototype stage?
Once the geometry is frozen, we move the part to CNC machining. Our 5-axis and mill-turn centers hold ±0.005 mm and finish to Ra 0.8–1.6 μm.
We quote and return a free DFM analysis within 12 hours, and production can start within 24 hours.
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