FDM vs Resin vs SLS

Pick the simplest process that meets the requirement: FDM for low-cost functional parts and big prototypes, resin (SLA/MSLA) for tiny features and smooth surfaces, and SLS (usually nylon) for strong complex geometry without support scars. This lesson compares what each process is physically doing, what that means for accuracy and strength, the real post-processing workload, and the safety differences so you can choose correctly the first time.

TL;DR

If you need big, cheap, durable parts fast: use FDM. If you need crisp tiny features or a paint-ready surface: use resin (and plan for wash/cure + PPE). If you need complex geometry without supports and tough, consistent nylon parts: choose SLS (often outsourced) and plan for powder handling.

FDM vs Resin vs SLSTopic-specific diagram for the concept, checks, and tradeoffs in this lesson.FDMStrong, fast draftsResinFine detailSLSProduction nylon
A quick visual map of the main decisions behind FDM vs resin vs SLS.

What each process is doing (and why it matters)

FDM melts a solid thermoplastic filament and lays down beads (roads) that cool and fuse to the layer below; this creates visible layer lines and strength that depends on bead bonding. Resin (SLA/MSLA) turns liquid photopolymer into solid by UV exposure; it can form very small features and smooth surfaces, but the plastic chemistry and post-cure strongly affect final toughness. SLS fuses nylon powder with a laser while unfused powder supports the part; this enables complex shapes without support structures, with a characteristic slightly grainy surface.

Fast picker: choose by requirement

  • Lowest cost per part, easiest setup, widest hobby access: FDM
  • Large parts and quick size/fit iterations: FDM
  • Fine text, sharp edges, miniatures, thin walls, smooth finish: resin (SLA/MSLA)
  • Best-looking small mechanical details without sanding: resin
  • Internal channels, lattices, complex geometry where supports would scar or be impossible: SLS
  • Tough nylon parts with more uniform properties (less layer-weakness drama): SLS (commonly a service)

Tradeoffs that show up on real parts

Surface finish
FDM: layer lines and seam; Resin: smooth and crisp; SLS: matte/grainy but consistent.
Small features
FDM: limited by nozzle width and layer height; Resin: best for tiny features; SLS: good, but edges are not as sharp as resin.
Strength behavior
FDM: strongest along filament, weaker between layers; Resin: can be brittle unless using tough/flexible resins and proper cure; SLS: tough nylon with relatively even strength.
Supports
FDM: needed for overhangs, can scar; Resin: almost always needs supports and leaves nibs; SLS: no supports (powder is the support).
Post-processing time
FDM: remove supports, deburr/sand if needed; Resin: drain, wash, dry, remove supports, post-cure; SLS: depowdering/cleaning, optional smoothing/dye.
Dimensional accuracy
All can be accurate, but the failure modes differ: FDM shrinks/warps and hole sizes skew; resin can swell from trapped resin/overcure; SLS has predictable shrink and powder-texture edges.

Common materials you will encounter

PLA (FDM) easy
  • Low warp
  • Good stiffness
  • Simple printing
  • Lower heat resistance
  • Can creep under load
PETG (FDM) medium
  • Tougher than PLA
  • Better heat resistance
  • Good for functional parts
  • Stringing
  • Less crisp detail than PLA
ABS/ASA (FDM) harder
  • Heat resistance
  • Durable
  • Good for outdoor (ASA)
  • Warping
  • Fumes
  • Often needs enclosure
Standard photopolymer (resin) medium
  • High detail
  • Smooth finish
  • Brittle vs thermoplastics
  • Requires wash and cure
Tough/flexible resin harder
  • Improved impact resistance
  • Better snap-fit behavior
  • More sensitive settings
  • Can be expensive
Nylon PA12 (SLS) harder
  • Tough
  • Good fatigue resistance
  • No supports needed
  • Usually outsourced
  • Slightly grainy surface

Symptoms you chose the wrong process (and what to do)

Fine details keep disappearing, corners look rounded, tiny text is unreadable

Likely cause: FDM bead width/layer height are larger than the feature; molten plastic also rounds sharp corners

Fix: Switch to resin for detail work, or redesign features to exceed nozzle/layer limits (bigger text, thicker ribs)

Part looks good but snaps along a layer line in use

Likely cause: FDM anisotropy: weak inter-layer bonding or load is pulling layers apart

Fix: Reorient so layers run along the load, increase wall count, improve temperature/flow for bonding, or choose SLS nylon for more uniform toughness

Visible faces are ruined by support marks or are impossible to support cleanly

Likely cause: FDM and resin supports touch the surface; complex internal geometry can make supports unavoidable

Fix: Reorient to hide supports, split the model for clean mating surfaces, or choose SLS to avoid supports entirely

The print is done, but finishing dominates the project time

Likely cause: Resin wash/cure and support cleanup, or FDM sanding/filling to chase a smooth surface

Fix: Match process to finish requirement: resin for ‘out of printer’ smoothness (accepting wash/cure), FDM for quick utility, or outsource SLS for complex parts with minimal support cleanup