FDM and SLA are the two dominant desktop 3D printing processes, and they’re genuinely different tools for different jobs. Choosing the wrong one leads to parts that are too brittle, too expensive, or both. Here’s the honest breakdown from a shop that runs FDM daily and ships SLA parts through partners.
- FDM wins on: strength, cost, engineering plastics (PLA/PETG/ABS/ CF-nylon), large parts, functional prototypes, production runs.
- SLA wins on: surface finish, fine detail (<0.5 mm features), jewelry masters, dental models, castable patterns, display-grade minis.
The fundamental difference
FDM (fused deposition modeling) melts a plastic filament and squirts it through a heated nozzle, building the part line by line, layer by layer. SLA (stereolithography) shines UV light into a vat of liquid photopolymer resin, solidifying a thin layer at a time. Same end goal — very different physics.
| Dimension | FDM | SLA |
|---|---|---|
| Material | Solid plastic filament (thermoplastic) | Liquid photopolymer resin |
| Process | Heat + extrude | UV light + chemical cure |
| Finish (stock) | Visible layer lines | Near-smooth |
| Min feature size | ~0.4 mm (nozzle width) | ~0.1 mm |
| Part strength | High, isotropic-ish | Medium, anisotropic, often brittle |
| Typical build size | Large (300 × 300 × 400 mm common) | Small to medium (~150 × 150 × 180 mm) |
| Cost per cm³ | $0.035–$0.125 | $0.15–$0.50+ |
| Post-processing | Optional — parts work as-is | Mandatory (wash + UV cure) |
| Handling | Safe, handle with bare hands | Resin is toxic uncured; gloves required |
| Outdoor / long-term UV | Good (PETG, ASA) | Poor — cured resin yellows and cracks |
FDM — strength at low cost
FDM prints are made of real engineering thermoplastics: PLA, PETG, ABS, nylon, polycarbonate, carbon-fiber-reinforced versions of all of the above. Those materials have decades of real-world use — you’re not using a novel material, you’re using a plastic you could buy in pellet form and injection mold tomorrow.
Where FDM shines
- Functional prototypes you’ll stress-test — FDM parts bend, impact, hold threads, and take load.
- Large parts — a 300 mm jig prints on one of our printers overnight. On SLA it wouldn’t fit.
- Low-volume production — at $3–$15/part, FDM scales to dozens or hundreds of units without tooling.
- Structural parts — PET-CF and nylon handle real mechanical load.
- Outdoor / UV / chemical exposure — PETG, ASA, nylon survive conditions that destroy SLA parts.
Where FDM loses
- Layer lines are visible. Typical 0.2 mm layers show up as stripes under raking light. Sanding and painting fix it, but that’s extra cost/time.
- Fine detail is limited. Feature minimums are bound by nozzle width (0.4 mm typical). Tabletop miniatures look blobby in FDM; they look crisp in SLA.
- Complex internal geometry with overhangs needs support material that leaves marks.
SLA — surface finish and detail
SLA parts come off the printer with a near-glass finish (after wash and cure). Tiny features — a 0.2 mm engraved logo, a 0.3 mm wall on a miniature’s sword, a tooth crown — resolve cleanly. That’s the win.
Where SLA shines
- Display-grade miniatures (D&D, Warhammer, character figures). FDM can’t match SLA on surface quality at this scale.
- Jewelry masters — castable resins burn out cleanly in a furnace for lost-wax casting.
- Dental models and aligners — biocompatible resins are certified for intraoral use.
- Translucent / clear parts — clear resin is genuinely clear; FDM “clear” is frosted at best.
- Patterns for silicone molding — smooth SLA surfaces give sharp mold shells.
Where SLA loses
- Brittleness. Standard SLA resins snap where FDM PLA would crack and where PETG would flex. “Tough” resins help but never match nylon.
- UV degradation. Sunlight yellows and embrittles most cured resins over months.
- Cost per cm³. Resin is 3–10× the price of filament.
- Messy workflow. Uncured resin is toxic, sticky, and requires gloves, wash stations, and UV cure chambers.
- Small build volume. Most desktop SLA tops out around 150 × 150 × 180 mm.
Process decision tree
Ask yourself, in order:
- Will this part take mechanical load, impact, or heat?
→ FDM. Real plastics beat brittle resin for anything functional. - Does this part have features smaller than 0.5 mm that need to look crisp?
→ SLA. FDM’s 0.4 mm nozzle can’t resolve that detail. - Is the part larger than 150 mm in any dimension?
→ FDM. Won’t fit most SLA printers. - Does it need to live outdoors or under sun?
→ FDM with PETG or ASA. - Is this a casting pattern (jewelry, dental)?
→ SLA with castable resin. - Is budget the top priority?
→ FDM. Lower cost per part, almost always.
Cost comparison on the same 50 cm³ part
| Process + Material | Cost | Finish | Strength |
|---|---|---|---|
| FDM, PLA | $20 (our minimum kicks in) | Layer lines visible | Medium, brittle |
| FDM, PETG | $20 | Layer lines visible | High, tough |
| FDM, PET-CF | $27.50 | Matte / fibrous | Very high, stiff |
| SLA, standard resin | $40–$60 | Near-smooth | Medium, brittle |
| SLA, tough / engineering resin | $60–$90 | Near-smooth | Medium-high |
For this part: FDM PETG gives you the best cost / strength ratio. SLA is only worth the premium if you need the finish quality.
Hybrid strategy: use both
Real workflows often mix processes. Our most sophisticated customers do this:
- Prototype in FDM to iterate fast and cheap. Validate geometry across 5–10 revisions at $10–$20 each.
- Final display piece in SLA once the geometry is locked. Spend the premium on the one that matters.
- Production in FDM if volumes support it — even a 50-unit run of a mechanical part is $200–$600 in FDM vs. thousands in SLA.
What we run at TAKT 3D
Our San Diego shop is an FDM-first operation because ~90% of the customer jobs we see are functional parts, brackets, enclosures, jigs, and low-volume production where FDM wins decisively. We partner with SLA shops locally for the 10% of jobs that actually need resin — and we’ll tell you up front when that’s your job.
Materials we stock for FDM: PLA, PETG, ABS, TPU, PET-CF. See per-material rates on our pricing page.
FDM vs SLA FAQ
Is SLA stronger than FDM?
No. Standard SLA resins are roughly 40–60 MPa tensile but brittle — they snap where FDM PETG or nylon would bend. “Tough” resins close the gap but add cost. For load-bearing parts, FDM with the right material is almost always stronger in real-world use.
Why do SLA parts look so much better than FDM?
Layer thickness. SLA routinely prints 25–50 micron layers; FDM’s standard is 200 microns (5–8× bigger). Smaller layers = less visible stepping = smoother finish.
Can FDM match SLA quality with post-processing?
Close, with sanding and painting. For cosmetic display purposes a well-finished FDM PLA print at 0.12 mm layers, sanded and primed, looks excellent. But the labor usually makes SLA cheaper on small parts.
Which is better for miniatures?
SLA, no contest — for tabletop minis under 50 mm tall. See our tabletop gaming page for what FDM can and can’t do at that scale.
Which is better for production?
FDM. Faster per-part throughput, cheaper per part, parallelizable across many printers. SLA batch times are slower and post-processing is serial.
Is one safer than the other?
Yes — FDM is substantially safer for home and office use. FDM materials are inert solids. SLA uses liquid resins that are skin-irritating and require gloves, ventilation, and proper disposal before cure.
Bottom line
If you need a functional part that works — FDM, almost every time. If you need a display-grade surface finish on a small detailed part — SLA. Most shops that push you toward one or the other aren’t being dishonest; they’re just optimizing for what they own.
Not sure which is right for your part? Upload it to our quote tool and we’ll tell you if FDM is the right call — and refer you out if it isn’t.