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.
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 (Fused Deposition Modeling) is the simplest and most common form of 3D printing. A printer feeds a spool of thermoplastic filament through a heated nozzle, melting it and depositing it layer by layer to build a part from the bottom up. When the plastic cools, it fuses to the layer below.
FDM is available everywhere — from home printers to industrial machines. The wide range of compatible materials and the sheer number of FDM service providers makes it the default choice for most everyday 3D printing needs.
How SLA Printing Works
SLA (Stereolithography) uses ultraviolet light to cure liquid photopolymer resin. A UV laser or light array exposes a thin layer of liquid resin, hardening it. The build platform then moves, and another layer of liquid resin is exposed. This process continues until the part is complete.
Because SLA uses light rather than a melting nozzle, it can achieve much finer resolution and smoother surfaces than FDM. The trade-off is that resin parts require post-processing (washing and curing), are generally more brittle than thermoplastic FDM parts, and resin printing is more common at professional studios than home shops.
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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