FDM vs SLA
Plastic vs resin.
Plastic vs resin.
Engineer vs precise.
Different strengths.
FDM extrudes molten thermoplastic — durable engineering plastics, large parts, functional prototypes. SLA cures photopolymer resin — fine detail, smooth surface, visual quality. They solve different problems.
01 · At a glance
Side-by-side summary.
Option A
FDM (Fused Deposition)
Molten thermoplastic extruded layer by layer. ABS, PC, nylon, Ultem, PEEK. Durable functional parts. Large build volumes (914×610×914 mm industrial). Visible layer lines.
Option B
SLA (Stereolithography)
UV laser cures photopolymer resin. Fine detail (0.1 mm features), smooth surface (Ra 2-5 µm). Limited to photopolymers — brittle, UV-sensitive. Typical build size <500 mm.
02 · Detailed comparison
Feature-by-feature breakdown.
| Attribute | FDM | SLA |
|---|---|---|
| Materials | Engineering thermoplastics | Photopolymer resins |
| Typical tolerance | ±0.2-0.5 mm | ±0.05-0.1 mm |
| Surface finish (Ra) | 15-30 µm (layer lines) | 2-5 µm |
| Minimum feature size | 1.2 mm walls, 2 mm holes | 0.1 mm features, 0.5 mm holes |
| Max build size | 914×610×914 mm (industrial) | 500×500×500 mm (largest) |
| Max part durability | Production-grade (Ultem, PEEK) | Prototype only (brittle) |
| UV stability | Good for most | Yellows and degrades |
| Temperature service | Up to 260°C (PEEK) | 80-120°C typical |
| Speed per cm³ | Moderate | Slow (laser traces) |
| Typical cost per part | $30-500 | $30-500 |
| Lead time | 3-7 days | 2-4 days |
| Best use | Functional testing, production parts | Visual prototypes, master patterns |
03 · Decision guide
When to choose each.
Choose FDM (Fused Deposition) when:
- Functional engineering prototypes
- Large parts (up to 914 mm)
- Aerospace Ultem 9085 parts
- Temperature-resistant applications
- Production-intent manufacturing
- Low-volume end-use parts
Choose SLA (Stereolithography) when:
- Visual prototypes with fine detail
- Master patterns for silicone molds
- Investment casting patterns
- Dental and medical models
- Jewelry prototypes
- Smooth cosmetic appearance
FAQ
Common questions.
Industrial FDM with engineering materials: yes. Ultem 9085 FDM parts are FAA-certified for aircraft interior production (not just prototypes). Ultem 1010 meets USP Class VI for medical. PEEK FDM for aerospace structural applications. Desktop FDM (hobbyist machines): no — not production quality. For FDM production: industrial machines only (Stratasys Fortus, BigRep, Markforged).
Standard SLA photopolymer resins are thermoset — cured permanently into rigid brittle structure. Unlike thermoplastics (ABS, PC), SLA resins don't yield gracefully — they fracture. Tough SLA resins exist (Formlabs Tough, Siraya Tenacious, etc.) with some improvement, but still inferior to thermoplastic toughness. For handling, drop-testing, impact loading: use FDM (ABS or PC) or SLS/MJF nylon.
Very. FDM layer lines are visible from 1 meter away — clearly "3D printed" appearance. Ra 15-30 µm typical. Post-processing: vapor smoothing (ABS with acetone) improves significantly. SLA layer lines virtually invisible, surface looks injection-molded. Ra 2-5 µm native, can polish to optical clarity. For cosmetic prototypes: SLA wins. For functional prototypes: FDM layer lines acceptable.
Industrial FDM: up to 914×610×914 mm in single build. Some large-format FDM goes to 2 meters. SLA: typically 500×500×500 mm maximum (largest commercial machines). For parts larger than SLA envelope: FDM or segmented build (print sections, bond). FDM is the primary large-part 3D printing process.
Most SLA resins yellow and become brittle with UV exposure. Indoor storage: 1-3 year useful life. Outdoor exposure: days to weeks. For UV-stable SLA, specialty resins available but limited range. For long-service parts requiring UV stability: FDM (ABS, PC, ASA — latter specifically UV-stable), SLS/MJF (nylon UV-stable with additives), or conventional manufacturing. Don't use SLA for long-term outdoor applications.
Similar cost per volume for typical parts. Small FDM ABS part: $30-80. Same part in SLA: $30-100. Medium FDM: $100-300. SLA: $100-400. Large FDM: $300-1500. Large SLA: $500-3000 (where possible). Material cost drives difference — Ultem FDM is expensive ($200-500/kg), premium SLA resins $100-300/kg. For prototype validation, both cost similar total. Choose based on properties needed, not cost.
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