Combined 3D Services
SLA vs FDM 3D Printing: Which Should You Choose?
By Mike Moussa, PE — We run both SLA and FDM printers daily. Here’s when each one makes sense, based on real projects — not marketing brochures.
The Quick Answer
Use FDM when you need strong, functional parts at the lowest cost. Use SLA when you need smooth surfaces, fine details, or tight tolerances. That covers 90% of decisions.
FDM (Fused Deposition Modeling)
How It Works
A heated nozzle melts plastic filament and deposits it layer by layer. Think of it like a very precise hot glue gun moving in 3D.
Strengths
- Strongest parts — FDM parts in ABS, Nylon, or Polycarbonate are genuinely strong. You can make load-bearing brackets, functional enclosures, and production fixtures.
- Cheapest per part — material costs are low, print speeds are fast, and failures are cheap.
- Largest build volumes — FDM printers can build parts up to 24″+ in some cases.
- Wide material selection — PLA, ABS, PETG, Nylon, PC, ULTEM, carbon-fiber filled, and more.
- Easiest to iterate — change the file, hit print, have a new part in hours.
Limitations
- Visible layer lines — FDM parts have a characteristic ribbed texture. Post-processing (sanding, vapor smoothing) helps but adds time and cost.
- Lower detail resolution — minimum feature size is typically 0.5-1mm. Fine text, thin walls, and small holes are challenging.
- Anisotropic strength — parts are weaker in the Z direction (between layers). Orientation matters a lot.
- Support removal marks — where support structures were removed, surfaces will be rough.
SLA (Stereolithography)
How It Works
A UV laser (or LED array) cures liquid photopolymer resin one layer at a time. Each layer is incredibly thin (25-100 microns), producing smooth, detailed parts.
Strengths
- Smooth surfaces — SLA parts come off the printer nearly injection-mold smooth. Minimal post-processing needed.
- Fine details — features as small as 0.1mm are possible. Ideal for jewelry, dental, and precision parts.
- Tight tolerances — ±0.002″ is achievable (FDM is typically ±0.005-0.010″).
- Isotropic properties — unlike FDM, SLA parts have similar strength in all directions.
- Clear parts — clear resins produce genuinely transparent parts (after polishing).
Limitations
- Brittle — most SLA resins are more brittle than FDM plastics. They crack under impact rather than flexing.
- UV sensitivity — resin parts degrade in direct sunlight over time. Not ideal for outdoor use.
- Higher cost — resin is more expensive than filament, and post-processing (washing, curing) adds labor.
- Smaller build volume — most SLA printers max out around 6-10″ in any direction.
- Post-processing required — parts need washing in isopropyl alcohol and UV curing after printing.
Head-to-Head Comparison
| Factor | FDM | SLA |
|---|---|---|
| Surface finish | Visible layers | Near-smooth |
| Strength | Strong, tough | Brittle |
| Detail resolution | Good (0.5mm+) | Excellent (0.1mm+) |
| Cost per part | Lower | Higher |
| Build size | Large (24″+) | Small-medium |
| Material variety | Wide | Limited |
| Tolerances | ±0.005-0.010″ | ±0.002-0.005″ |
| Outdoor use | Yes (ABS, ASA) | Limited |
| Turnaround | 1-2 days | 2-3 days |
Real-World Examples
When We Use FDM
- Functional prototypes that need to survive testing
- Production fixtures and jigs for factory floors
- Large enclosures and housings
- Parts that need to snap, flex, or take impact
- Anything in Nylon, PC, or ULTEM
When We Use SLA
- Presentation models for investor meetings
- Master patterns for urethane casting molds
- Parts with fine text, logos, or surface textures
- Clear or transparent components
- Medical and dental models
Still Not Sure?
Tell us what the part needs to do, and we’ll recommend the right process. We run both SLA and FDM daily — no bias toward either.