We run all three processes in-house: FDM, SLA, and SLS. Each one is great at something and terrible at something else. Picking the wrong one costs you time, money, and sometimes a part that fails in the field. Here's the no-marketing version.

FDM (Fused Deposition Modeling)

Plastic filament melted and extruded layer by layer. Materials: PLA, PETG, ABS, ASA, nylon, PC, polycarbonate, carbon-fiber composites.

Use FDM for:

Jigs, fixtures, and end-of-arm tooling for production
Large parts (build volumes up to 600×600×600 mm)
Functional prototypes where exact strength and surface finish don't matter
Cheap iteration — a $5 PLA part lets you test 10 designs in a week
Outdoor / UV-exposed parts (ASA)

Avoid FDM for:

Small fine-detail parts (layer lines limit feature resolution)
Parts under load along the Z axis (anisotropic — strong in X-Y, weak in Z)
Cosmetic parts that customers will see (visible layer lines)
Pressure-tight or watertight parts (porosity at layer interfaces)

SLA / MSLA (Resin)

Liquid photopolymer cured layer by layer with a laser or LCD. Materials: standard resin, tough/ABS-like, flexible, high-temp, dental, casting (burn-out) resins.

Use SLA for:

High-detail visual prototypes (50µm layer height; you can't see the lines)
Casting masters (lost-resin/wax patterns for investment casting)
Concept models for marketing and sales
Master patterns for silicone molds
Small mechanical parts that need crisp features

Avoid SLA for:

Long-term outdoor / UV exposure (resins yellow and embrittle)
Functional load-bearing parts in normal resin (brittle)
Large parts (build volume and post-cure cracking get worse with size)
Anything food-contact unless using a certified resin (most aren't)

SLS (Selective Laser Sintering)

Nylon (PA12, PA11, glass-filled, carbon-filled) sintered layer by layer in a powder bed. No support material — the unsintered powder supports overhangs.

Use SLS for:

Functional, near-isotropic nylon parts
Bridge production (50–5,000 parts before tooling pays off)
Living hinges, snap-fits, and parts that need real plastic-like behavior
Complex geometries with internal channels (no supports to remove)
Lattice structures and weight-critical parts

Avoid SLS for:

Cosmetic class-A surfaces (powdery surface finish unless dyed/vapor-smoothed)
Tight tolerances (±0.005" is a stretch goal, not a default)
Single low-volume parts where setup cost dominates
Transparent or color-critical parts (post-process dyeing only)

The quick decision tree

Is the part bigger than a softball? → FDM (or skip 3D printing entirely and machine it)
Does the part need to look perfect for a customer or photo shoot? → SLA
Does the part need to take real load and be plastic-like? → SLS
Is it a jig or fixture for the shop floor? → FDM
Is it a casting master or detail prototype? → SLA
Bridge production of 100 functional parts? → SLS

Cost comparison (rough, per part)

Same 50mm × 50mm × 25mm bracket, single quantity:

FDM (PLA): $8–$15
FDM (nylon CF): $25–$45
SLA (standard resin): $20–$40
SLA (tough resin): $35–$70
SLS (PA12): $40–$80
CNC (6061 aluminum): $80–$200

Volume changes everything. At 1,000 parts, SLS becomes very competitive with injection molding for low-volume nylon parts (no tooling cost, no minimum order).

Post-processing

FDM: support removal, sand, vapor-smooth (ABS only), paint, threaded inserts
SLA: wash, UV cure, sand, polish, paint, dye
SLS: bead blast, vapor smooth, dye (black is most reliable), threaded inserts

What to send us with your 3D print RFQ

STL or STEP file
Material spec or end-use description (we can recommend)
Quantity and delivery date
Tolerance and surface finish requirements (be honest — tighter costs more)
Any post-processing (paint color, threaded inserts, tapping)

We've helped customers go from FDM prototype to SLS bridge run to CNC production tooling without changing shops. If you're not sure which process fits, send us the file — we'll tell you what we'd print and why, even if it's not the most expensive option.