3D printing comparison: FDM vs SLA vs SLS vs MJF vs metal PBF

The five main processes fall into three additive families: material extrusion, vat photopolymerization, and powder bed fusion.

• Fused deposition modeling (FDM), also called fused filament fabrication (FFF), pushes thermoplastic filament through a heated round nozzle and compresses each layer onto the one below. Overhangs steeper than 45 degrees from vertical need printed supports.
• Stereolithography (SLA) uses an ultraviolet laser with a 30 to 140 micron spot to trace and cure thin slices in a tank of liquid photopolymer resin. Supports are printed with the part, removed by hand after solvent washing, and the part is post-cured in an ultraviolet chamber.
• Selective laser sintering (SLS) uses a laser to fuse thin layers of heated polymer powder. Because the surrounding unsintered powder supports every layer, no support structures are needed.
• Multi Jet Fusion (MJF) is a polymer powder bed process where an inkjet array jets a fusing agent onto the part area and a detailing agent around the edges before heating elements fuse the layer. Like SLS, the powder bed supports the part so no printed supports are required.
• Direct metal laser sintering (DMLS) and selective laser melting (SLM) use a high-power laser in an inert, heated chamber to fuse or melt metal powder. For design purposes, DMLS and SLM are treated as the same process. Unlike polymer powder beds, metal parts must always be anchored to the base plate with welded metal supports to counter high thermal stress and warping.

Your material and loading requirements narrow the choice quickly.

FDM prints real thermoplastics, including PLA, ABS, nylon (PA), and flexible TPU. PLA prints easily with good visual quality but has low impact strength. ABS is stronger but prone to base-layer warping as it cools. Nylon offers high strength and wear and chemical resistance, though it absorbs humidity. Because FDM lays down round-ended beads, the joints between layers form small valleys that concentrate stress. That makes FDM parts anisotropic and weaker across the layers than along them.

SLA cures thermoset photopolymers, including specialty castable resins for investment casting patterns. Because the layers bond chemically during printing, SLA parts are isotropic and orientation does not change their mechanical properties. However, standard SLA resins only imitate engineering plastics. They are generally brittle, prone to creep, and degrade in ultraviolet light and humidity, making them unsuitable for functional loaded parts.

SLS and MJF print functional thermoplastics, primarily nylon (polyamide), TPU, and polypropylene. SLS also runs glass-, mineral-, and carbon-filled nylons, while MJF offers a full-color nylon grade and produces consistent, isotropic mechanical properties. Both processes yield strong, durable parts suited for end-use loads, snap-fits, and living hinges.

DMLS and SLM print structural metals, including austenitic stainless steel (316L), precipitation-hardening stainless steel (17-4 PH), titanium (Ti-6Al-4V), nickel superalloys (Inconel 718), casting-grade aluminum alloys, cold-work tool steels, and pure copper (which is fair to print due to reflectivity and conductivity). Final metal parts are near fully dense, with internal porosity below 0.2 to 0.5 percent. Tensile strength is comparable to wrought metal, though fatigue strength is generally lower due to surface roughness and trace porosity.

Published tolerances and minimum feature sizes come from individual manufacturing services and vary by machine, material, and geometry. Always confirm critical dimensions with your shop.

SLA holds the tightest tolerances and finest details of the five processes. One service publishes dimensional tolerances of ±0.002 in (0.051 mm) in the X-Y plane and ±0.005 in (0.127 mm) in the Z build direction for the first inch plus 0.1 percent, while another cites ±0.005 to ±0.012 in (0.127 to 0.305 mm) depending on platform. Minimum features reach down to 0.0025 in (0.063 mm) at micro resolution or 0.010 in (0.254 mm) in X-Y at normal resolution. As-printed SLA surfaces are smooth at about 60 to 120 microinches Ra away from support nibs, with layer thicknesses from 25 to 200 microns.

FDM is the least accurate of the five processes and leaves a visible layer texture. Desktop and industrial layers run from 150 to 400 microns, or 0.008 to 0.013 in (0.203 to 0.330 mm) by one service's defaults. That service publishes a minimum positive feature and hole size of 0.04 in (1.016 mm) and an as-printed surface roughness of 250 to 900 microinches Ra (6.35 to 22.86 microns Ra). Vertical holes print undersized because the nozzle compresses the bead, and the first layer flares out into an elephant's foot unless you add a 45 degree chamfer or radius to build-plate edges.

SLS and MJF sit in the middle on tolerances and leave a grainy, satin matte surface. SLS prints in roughly 0.1 mm (100 micron) layers and MJF in 80 micron layers. Depending on the service, published SLS tolerances are ±0.3 mm (0.012 in) plus ±0.05 mm per additional 25 mm, ±0.010 in (0.254 mm) plus 0.1 percent, or ±0.015 in (0.381 mm) for nylon 12. One service holds ±0.012 in (0.305 mm) plus 0.1 percent on MJF, with minimum walls and features of 0.02 in (0.508 mm), which is finer than its 0.03 in (0.762 mm) SLS limit. As-printed roughness is 250 to 520 microinches Ra for SLS and 250 to 560 microinches Ra for MJF; bead blasting is standard, MJF parts are usually dyed black for uniform color, and vapor smoothing can bring black nylon down to 64 to 100 microinches Ra on request.

DMLS and SLM build in 20 to 50 micron layers and hold ±0.1 mm (0.004 in) on a typical machine, or ±0.003 in (0.076 mm) in X-Y and ±0.006 in (0.152 mm) in Z for the first inch plus 0.1 percent at one service. Recommended minimums are 0.4 mm (0.016 in) walls, 0.6 mm (0.024 in) isolated features, and 1.5 mm (0.059 in) holes. As-printed metal surfaces measure 8 to 10 microns Ra (or 200 to 1000 microinches Ra by another publisher); tighter tolerances and smoother mating faces require secondary CNC machining or polishing.

Match the process to the part's job, volume, and geometry.

• Choose FDM for quick, low-cost prototypes, jigs, fixtures, brackets, and simple enclosures where visible layer lines and modest accuracy are acceptable. For repeat orders that must match in color and layer height, specify a branded industrial filament rather than general-purpose material.
• Choose SLA for high-precision form-and-fit testing, intricate visual models, and investment casting patterns. SLA resin costs more per volume than FDM filament, and heavy support requirements can make complex orientations uneconomical. If a part exceeds a desktop machine's 145 by 145 by 175 mm (5.7 by 5.7 by 6.9 in) envelope or an industrial 29 by 25 by 21 in (736 by 635 by 533 mm) frame, print it in sections and bond them with a 5- to 30-minute epoxy.
• Choose SLS or MJF for functional polymer prototypes and small-series production runs of roughly 1 to 1,000 parts without tooling costs. Because parts need no supports, they nest densely in the powder bed, making both processes more economical than FDM for larger runs of complex parts. Pick MJF when you want isotropic strength and finer 0.02 in (0.508 mm) features within an 11.1 by 14.9 by 14.9 in (282 by 378 by 378 mm) box. Pick SLS when you need glass- or carbon-filled nylon or a larger build envelope up to 700 by 380 by 580 mm (27.6 by 15.0 by 22.8 in). Above roughly 1,000 parts, injection molding typically takes over.
• Choose DMLS or SLM when a metal part's geometry justifies the process. Geometric complexity adds almost nothing to the build cost, making metal powder bed fusion ideal for consolidated assemblies, topology-optimized brackets, internal cooling channels, and lattices. Plain, blocky shapes designed for traditional machining are rarely economical to print in metal.

Every 3D printing route has geometry traps that cause warping, cracking, or failed builds. Applicable standards include ISO/ASTM 52911-1 for laser powder bed fusion of metals and ISO/ASTM 52911-2 for laser powder bed fusion of polymers.

• Hollow parts and drain holes: In SLA, SLS, and MJF, any hollowed section traps liquid resin or loose powder unless you provide escape holes of at least 3.5 mm (0.138 in) diameter. In SLA, trapped uncured resin builds pressure during curing, causing cupping, cracking, or part explosion. For non-functional SLA models, keep hollowed walls at least 2 mm (0.079 in) thick.
• Warping and wall thickness: In SLS and MJF, high process temperatures cause thick or uneven parts to shrink and warp as they cool. Keep walls near a uniform 0.125 in (3.18 mm) and hollow thick sections to a 0.100 to 0.125 in (2.54 to 3.18 mm) shell. For flat or broad polymer parts over 7 in (178 mm), use a filled nylon or a large-frame SLS machine. In DMLS and SLM, keep solid metal sections to 10 mm (0.394 in) or less to prevent thermal distortion and cracking.
• Overhangs and bridges: Keep unsupported FDM overhangs within 45 degrees of vertical and horizontal bridges under 5 mm (0.197 in). In DMLS and SLM, overhangs up to 50 degrees from vertical can print unsupported, and horizontal holes should be shaped like teardrops. In SLA, angle the part to minimize the 2D cross-section peeled from the tank on each layer, keep wide bridges under 21 mm (0.827 in), and face cosmetic surfaces upward away from supports.
• Pins, holes, and threads: Across all five processes, modeled threads rarely work well as printed due to surface roughness or resolution limits; tap holes after printing or install threaded inserts. On FDM, never print threads smaller than M5 (5 mm nominal diameter), keep vertical pins at least 5 mm (0.197 in) in diameter so they receive infill rather than perimeter-only walls, and plan to drill critical vertical holes to size.