FDM · SLS · Additive Manufacturing

FDM vs SLS 3D Printing — Additive Manufacturing Comparison

Updated: 2026-05-13 Category: AM Process Comparison Typical use: Prototyping · Production Editorial: KunststoffWissen

Both processes are layer-by-layer additive manufacturing for thermoplastics. The principle differs fundamentally: FDM extrudes melted filament along toolpaths; SLS fuses powder with a scanning laser. The differences in physics drive all the property and application differences.

Direct Process Comparison

Aspect	FDM (Fused Deposition)	SLS (Selective Laser Sintering)
Process principle	Filament melted + deposited	Powder fused by laser
Layer adhesion	Anisotropic (Z = 70–85 % of X/Y)	Isotropic
Surface finish	Visible layer lines (50–300 μm)	Slightly rough but uniform
Support structures	Required for overhangs	Not needed (powder supports)
Material variety	Very wide (PLA, PETG, ABS, PA, PEEK)	Limited (mostly PA11, PA12, TPU)
Material cost	EUR 20–80/kg (PLA-PA), EUR 500–1,500 (PEEK)	EUR 50–150/kg standard
Equipment cost	$300 desktop – $100k industrial	$50k–500k+ (industrial only)
Build volume	200×200×200 mm to 1×1×1 m+	300×300×300 to 700×400×500 mm
Resolution	100–400 μm layer	60–100 μm layer
Print speed	20–80 cm³/h typical	10–50 cm³/h
Typical applications	Prototypes, jigs, fixtures	End-use parts, complex internal channels

When to Choose Which

Choose FDM for: Rapid prototypes (visible same-day or next-day), jigs and fixtures, low-cost large parts, material experimentation (wide filament variety), in-office printing for design teams. Choose SLS for: End-use production parts requiring isotropic strength, complex internal channels (no support residue), small batch series (10–1,000 parts), aerospace and medical (PA11, PA12 are industry-accepted). SLA (stereolithography) is a third option: finest surface finish, smallest features — for dental, jewelry, micro-fluidics.

FAQ — Frequently Asked Questions

When is FDM strong enough for end-use parts?

For loads in print-plane direction: FDM parts in PA-CF or PETG achieve 60–80 % of injection-molded strength — adequate for many functional parts. For loads in Z-direction: layer adhesion limits performance to 30–50 % of bulk material. Design parts so primary loads run in X/Y. For omnidirectional loading or critical structural applications, SLS gives 90–100 % of bulk material strength isotropically.

Why is SLS more expensive but less material-flexible?

SLS materials must be specifically designed: spherical powder particles, controlled particle size distribution (typically 40–80 μm), thermal stability window between sintering and melting. Manufacturing this powder is expensive (atomization, sieving). FDM uses filament that's simpler to make (extrusion + spool). Number of SLS-compatible polymers: ~15 commercial. Number of FDM-compatible filaments: 200+. SLS pays off for production volumes; FDM wins for diverse small-volume work.

Surface finish — which is better post-processing?

FDM: Visible layer lines require post-processing (sanding, vapor smoothing, painting). With effort, can achieve near-injection-molded surface. SLS: Naturally smoother but slightly grainy from powder particles. Bead-blasting + dyeing achieves uniform appearance. For visual aesthetics: SLS is closer to finished out-of-printer; FDM requires more work. For functional surfaces (slip, sealing): both need attention.

Recycling — can powder/filament be reused?

SLS unsintered powder: ~50 % can be recycled and blended with virgin (refresh rate). After 3–5 cycles of recycling, properties degrade (powder aging from heat exposure in build chamber). Major recyclers (Sintratec, EOS) refresh practices. FDM scrap: failed prints can be ground and re-extruded (filament recyclers exist, e.g. ReDeTec, Felfil). Practical recycling for both is limited but improving — closed-loop within a print farm is common.

Production economics — when does AM beat injection?

Rule of thumb: AM is competitive with injection molding when production volume is below the cost of injection tooling divided by the cost difference per part. Example: injection tool $25k, AM saves $5 per part vs molding cost. Break-even at 5,000 parts — below that AM is cheaper. Modern industrial SLS (HP MJF, EOS P 500) achieves cost-per-part of EUR 1–10 for medium parts — competitive with low-volume injection. FDM rarely competes economically with injection for >1,000 parts.