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
Need big, cheap, durable parts quickly? Pick FDM. Need crisp tiny features or a paint-ready surface? Pick resin (SLA/MSLA) and plan for wash + cure plus PPE. Need tough nylon parts with complex geometry and no support scars? Pick SLS (often outsourced) and plan for powder cleanup.
What each process physically does (and what that changes on the part)
FDM melts solid thermoplastic filament and lays it down as beads (“roads”) that cool and fuse to the layer below. That bead-by-bead build creates visible layer lines, and strength depends heavily on how well layers bond. Resin (SLA/MSLA) uses UV light to solidify a liquid photopolymer. It can produce very small features and smooth surfaces, but final toughness depends on the resin chemistry and the wash/cure process. SLS uses a laser to fuse nylon powder while the unfused powder supports the part during printing. You get complex shapes without support structures, with a typical matte, slightly grainy surface.
Fast picker: choose by the thing you actually need
- Lowest cost and simplest workflow for most hobby parts: FDM
- Big prototypes and fast size/fit iterations: FDM
- Tiny text, sharp edges, miniatures, thin walls, smooth surfaces: resin (SLA/MSLA)
- Small parts that should look “finished” without sanding: resin
- Internal channels, lattices, and geometry that supports would scar or block: SLS
- Tough nylon parts with more even strength than layer-based prints: SLS (commonly via a service)
Tradeoffs you’ll see on real prints
- Surface finish
- FDM: visible layer lines and a seam; Resin: smooth with crisp detail; SLS: matte/grainy but uniform.
- Small features
- FDM: limited by nozzle width and layer height; Resin: best for tiny features; SLS: good, but less razor-sharp than resin.
- Strength behavior
- FDM: strongest along the extruded roads, weaker between layers; Resin: can be brittle without the right resin and cure; SLS: tough nylon with relatively even strength.
- Supports
- FDM: needed for many overhangs and can scar faces; Resin: usually required and leaves support nubs; SLS: no supports because the powder holds the part.
- Post-processing time
- FDM: remove supports and clean edges; Resin: drain, wash, dry, remove supports, then post-cure; SLS: depowder/clean, then optional smoothing or dye.
- Dimensional accuracy
- All can be accurate, but they fail differently: FDM can warp and undersize holes; resin can swell from trapped resin or overcure; SLS has predictable shrink with softened edges from powder texture.
Common materials you’ll run into
- Low warping for reliable prints
- Stiff parts for prototypes and fixtures
- Straightforward settings and handling
- Lower heat resistance in warm environments
- Can creep under constant load over time
- Tougher feel than PLA for many functional parts
- Better heat resistance than PLA
- Good general-purpose durability
- More stringing and cleanup
- Less crisp fine detail than PLA in many setups
- Higher heat resistance than PLA/PETG
- Durable parts with good impact resistance
- Better outdoor stability with ASA
- More warping and shrink behavior
- Fumes require ventilation
- Often needs an enclosure for consistent results
- Very high detail and sharp features
- Smooth, paint-friendly surfaces
- More brittle than many thermoplastics
- Requires wash and post-cure steps
- Improved impact resistance over standard resins
- Better behavior for snap fits and flexing features
- More sensitive to exposure and support settings
- Can be expensive
- Tough parts suitable for functional use
- Good fatigue resistance for repeated loading
- No support structures needed for overhangs
- Often outsourced rather than printed at home
- Matte, slightly grainy surface texture
Signs you picked the wrong process (and the fastest fix)
Fine details keep disappearing, corners look rounded, tiny text is unreadable
Likely cause: The FDM bead width and layer height are larger than the features, and molten plastic rounds sharp corners
Fix: Use resin for detail work, or redesign so features exceed nozzle/layer limits (larger text, thicker ribs)
Part looks good but snaps along a layer line in use
Likely cause: FDM anisotropy: the load is separating layers, or inter-layer bonding is weak
Fix: Reorient so layers run with the load, increase wall count, tune temperature/flow for bonding, or move to SLS nylon for more uniform toughness
Visible faces are ruined by support marks or are impossible to support cleanly
Likely cause: FDM/resin supports must touch the surface, and some internal/complex geometry makes clean support placement impossible
Fix: Reorient to move supports to hidden faces, split the model for clean mating surfaces, or use SLS to eliminate supports
The print is done, but finishing dominates the project time
Likely cause: Resin support removal plus wash/cure time, or FDM sanding/filling to reach a smooth finish
Fix: Pick the workflow that matches the finish: resin for smooth surfaces (accept wash/cure), FDM for quick utility parts, or SLS for complex geometry with little support cleanup