FDM vs SLA vs SLS vs DLP: The Definitive Print Quality Comparison
Choosing the right 3D printing technology is not just about budget — it is about matching the process to the part requirements. A dental aligner demands different tolerances than a mechanical bracket. A display prototype needs different surface finish than a production jig. This guide breaks down four major technologies on the metrics that actually matter: surface quality, dimensional accuracy, mechanical performance, and total cost.
1. Quick Technology Overview
FDM (Fused Deposition Modeling)
A thermoplastic filament is heated and extruded through a nozzle, deposited layer by layer. The most widely used 3D printing technology in the world. Known for affordability, material variety, and ease of use. Layer lines are visible on the surface.
SLA (Stereolithography)
A UV laser traces each layer into a vat of liquid photopolymer resin, curing it one cross-section at a time. Produces extremely smooth surfaces and fine detail. Requires post-processing (washing, curing).
DLP (Digital Light Processing)
Similar to SLA, but instead of a laser tracing each layer, a digital projector flashes the entire layer simultaneously. Faster than SLA for solid cross-sections. Resolution is determined by the projector pixel size.
SLS (Selective Laser Sintering)
A high-power laser fuses powdered material — typically nylon (PA12) — layer by layer. No support structures needed because the surrounding powder supports the part. Produces strong, functional parts with a characteristic matte texture.
2. Surface Finish Comparison
| Technology | Typical Layer Height | Surface Roughness (Ra) | Visual Finish |
|---|---|---|---|
| FDM | 0.10 – 0.30 mm | 15 – 70 µm | Visible layer lines, staircase effect on curves |
| SLA | 0.025 – 0.10 mm | 2 – 15 µm | Near-injection-mold smooth, minimal post-processing |
| DLP | 0.025 – 0.10 mm | 3 – 20 µm | Very smooth, slight pixel texture visible under magnification |
| SLS | 0.06 – 0.15 mm | 8 – 16 µm | Uniform matte / slightly grainy texture, no layer lines |
Verdict: If surface finish is priority number one — SLA wins. DLP is extremely close. SLS is unexpectedly good due to the powder-based process eliminating visible layer lines. FDM is always the roughest, though vapor smoothing (for ABS) or filler primer can narrow the gap dramatically.
3. Dimensional Accuracy
| Technology | Typical Tolerance | Best-Case Tolerance | Key Accuracy Factors |
|---|---|---|---|
| FDM | ± 0.3 mm | ± 0.1 mm | Nozzle diameter, thermal expansion, bed adhesion |
| SLA | ± 0.1 mm | ± 0.025 mm | Laser spot size, resin shrinkage, overcure |
| DLP | ± 0.1 mm | ± 0.035 mm | Pixel size, resin shrinkage, light bleed |
| SLS | ± 0.2 mm | ± 0.1 mm | Powder particle size, thermal warping, laser calibration |
Verdict: SLA and DLP offer the tightest tolerances, making them the go-to for engineering fits, snap connections, and assemblies with tight clearances. FDM can achieve surprisingly good accuracy with careful calibration, but thermal effects (warping, shrinkage) are harder to control on large parts.
4. Mechanical Strength & Part Behavior
FDM — Anisotropic Strength
FDM parts are significantly weaker in the Z-axis (between layers) than in X/Y. A part loaded perpendicular to layer lines may fail at 30–50% of its rated tensile strength. This anisotropy is the single biggest limitation of FDM for functional parts.
Mitigation strategies: print orientation optimization, increased wall count, higher infill, and material selection (Nylon, CF-PETG, and polycarbonate offer better inter-layer bonding than PLA).
SLA/DLP — Isotropic but Brittle
Resin parts are nearly isotropic — strength is consistent in all directions. However, standard resins tend to be brittle compared to thermoplastics. Tough resins and engineering resins (like Formlabs Tough 2000 or Siraya Tech Tenacious) close this gap, but at 3–5x the material cost.
UV degradation is a real concern: uncured or poorly cured resin parts can become brittle over months of sun exposure. Always post-cure resin parts fully.
SLS — Best Mechanical Performance
SLS Nylon (PA12) parts are strong, flexible, and have excellent fatigue resistance. They hold up well under repeated loading — something FDM and resin parts struggle with. SLS is the preferred technology for functional prototypes, production jigs, and end-use parts.
🔧 Rule of thumb: If the part will bear load, experience vibration, or be exposed to heat — SLS Nylon or well-configured FDM (CF-PETG, PA-CF) will outperform resin every time. If the part needs to look perfect with fine details — SLA is the answer.
5. Support Structures
- FDM: Requires breakaway or soluble supports for overhangs beyond 45–60°. Support removal leaves marks that need sanding. Multi-material printers can use PVA (water-soluble) supports for cleaner results.
- SLA/DLP: All overhangs and islands need supports. Supports are thin and snap off, but leave small nubs (support marks) that require sanding. Orientation is critical — always orient to minimize supports on cosmetic faces.
- SLS: No supports needed — this is SLS's greatest advantage. The powder bed supports the part during sintering. Any geometry, any overhang, any internal channel — all print without supports.
6. Cost Per Part
| Technology | Machine Cost | Material Cost | Cost per cm³ | Post-Processing |
|---|---|---|---|---|
| FDM | $200 – $5,000 | $15 – 50/kg | $0.02 – 0.08 | Low (support removal) |
| SLA | $300 – $10,000 | $30 – 200/L | $0.05 – 0.20 | Medium (wash, cure, sand) |
| DLP | $200 – $8,000 | $25 – 150/L | $0.04 – 0.15 | Medium (wash, cure, sand) |
| SLS | $10,000 – $500,000 | $50 – 100/kg | $0.10 – 0.40 | Low (depowdering, bead blast) |
Verdict: FDM is cheapest per part for medium-to-large objects. SLA/DLP is competitive for small, high-detail parts (jewelry, dental, miniatures). SLS has the highest upfront cost but becomes economical at volume because parts can be nested densely in the powder bed with zero wasted support material.
7. Which Technology for Which Application
- Prototyping (visual): SLA or DLP — smooth surfaces, captures fine details
- Prototyping (functional): FDM with engineering filament or SLS Nylon
- End-use production parts: SLS for strength, FDM for large/low-cost
- Dental & jewelry: SLA or DLP — sub-50µm detail, castable resins
- Miniatures & figurines: SLA or DLP at 0.025mm layers
- Tooling, jigs, fixtures: FDM (CF-PETG or Nylon) or SLS
- Architecture models: FDM for large scale, SLA for presentation quality
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