FDM and SLA are the two most widely available 3D printing technologies. Both can produce custom parts from a digital file — but they work very differently and excel at very different things. Choosing the wrong technology for your project can mean wasted money, slower turnaround, or parts that don't perform as expected.
CoreXY printers running at 300–500mm/s are now standard at most US service bureaus, cutting FDM turnaround times by 40–60% compared to two years ago. On the resin side, MSLA (masked SLA) with 8K resolution has largely replaced traditional laser SLA at professional studios — delivering finer detail at lower cost per part. The core trade-offs in this guide still hold, but speed and quality differences have narrowed for many everyday project types.
This guide explains how FDM and SLA printing work, what they're each good at, and how to decide which is right for your specific project.
How FDM Printing Works
FDM melts plastic filament through a heated nozzle and deposits it in layers — simple in concept, and that simplicity is part of the appeal. Machines are widely available, materials are inexpensive, and build volumes can be large. Layer lines are visible on finished parts, which matters more for some applications than others. Most functional prototypes, brackets, and enclosures go out the door as FDM because nothing else comes close on cost and speed for that category of work.
The range of FDM-compatible materials has expanded considerably. Beyond basic PLA, shops now routinely run PETG, nylon, TPU, ASA, and carbon fiber composites — which means "FDM" no longer implies a fragile part. Engineering filaments can produce components with mechanical properties that hold up under real load.
How SLA Printing Works
SLA cures liquid photopolymer resin with UV light — either a laser tracing each layer, or (in the more common MSLA and DLP variants) a screen that exposes an entire layer at once. The platform indexes downward between layers, building the part from the bottom of the resin tank up. When it's done, parts need to be washed in isopropyl alcohol and post-cured under UV to fully harden the resin.
The practical result is surface quality that FDM can't match. Layer lines at 0.025–0.05mm resolve details that would simply disappear on a 0.2mm FDM layer. Resin parts are typically more brittle than thermoplastics and require more careful handling — that's the main trade-off. Where it matters most is anywhere the part needs to look good or capture fine geometry: dental models, jewelry, miniatures, consumer product housings.
Head-to-Head Comparison
| Factor | FDM | SLA / Resin |
|---|---|---|
| Cost (small part) | $10–$40 | $20–$80 |
| Surface finish | Visible layer lines | Smooth, glassy |
| Detail resolution | 0.1–0.3mm layers | 0.025–0.1mm layers |
| Material variety | Very wide | Growing fast |
| Part toughness | Good to excellent | Fair (brittle) |
| Build volume | Up to 1,000mm+ | Up to 400mm |
| Availability | Widely available | Professional studios |
| Lead time | Same day to 3 days | 1–3 days |
| Post-processing needed | Support removal | Wash + cure |
When to Choose FDM
FDM is the right choice when:
- You need a functional part that will be stressed, dropped, or used repeatedly
- You need engineering materials like PETG, Nylon, Polycarbonate, or PEEK
- You need a large part — FDM printers can handle build volumes that SLA machines can't match
- You're on a tight budget — FDM is almost always cheaper per gram
- You need same-day or next-day turnaround — FDM shops are far more common and faster
- Surface finish doesn't matter — internal parts, structural components, jigs, and fixtures
When to Choose SLA / Resin
SLA is the right choice when:
- You need fine detail — miniatures, jewelry, dental models, or small mechanical components
- You need a smooth surface finish — presentation models, consumer product prototypes
- Layer lines are unacceptable in the final part — visible surfaces, display models
- You need dental or medical parts — biocompatible resins are available for SLA
- You need castable patterns for lost-wax jewelry casting
- You're printing miniatures or tabletop gaming pieces
If you'd be happy with the part painted or sanded, choose FDM. If the raw surface quality matters (no sanding, must look finished), choose SLA. If you need it to take a beating, choose FDM. If you need to see fine details at close range, choose SLA.
What About SLS and Metal?
For strong, complex engineering parts without support structures, SLS nylon printing is often a better choice than both FDM and SLA. For metal components, metal 3D printing (DMLS/SLM) is the only option that delivers true metal properties.
See our full technology guide for a comparison of all five major 3D printing technologies. For a detailed head-to-head of SLS and MJF powder-bed nylon processes, see our SLS vs. MJF comparison. If you're weighing resin in more depth, our SLA resin printing guide covers materials, post-curing, tolerances, and when to choose resin over FDM.
Frequently Asked Questions
FDM is generally stronger in the XY plane, but has weaker layer adhesion in the Z direction (anisotropic). SLA parts are more isotropic but typically more brittle than FDM thermoplastics. For functional, stress-bearing parts, FDM with PETG or Nylon is usually the better choice.
Yes, typically. SLA resin costs more per gram than FDM filament, and SLA requires additional post-processing. For small, detailed parts, the premium is often worth it. For large parts, the cost difference becomes significant.
Yes. FDM prints painted well with acrylic or spray paint after light sanding and a primer coat. PLA is the easiest to paint and sand. If you need a painted finish, FDM can produce excellent results with the right post-processing.
FDM is faster for most simple parts. MSLA (masked SLA, used by most modern resin printers) can be faster for small detailed parts because it cures an entire layer at once. However, FDM has a much larger service provider network, meaning you can usually find same-day FDM service more easily than same-day SLA.
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