MJF vs SLS: Which Is Stronger, Faster and Better for 3D Printed Parts

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  MJF vs SLS at a glance
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  How MJF and SLS actually build a part
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  Strength: which process gives a tougher part
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  Speed: build time and real lead time
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  Surface finish and small features
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  Cost per part and where the crossover sits
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  When MJF is right, and when SLS is right

Both processes start with a roller spreading a thin layer of nylon powder across a heated bed. The difference is how that layer gets fused. In MJF, a printhead deposits a fusing agent where the part should be, then an infrared lamp passes over the whole bed and the treated powder absorbs the heat and melts together. Untreated powder stays cool and acts as support.

SLS uses no agent. A laser traces the cross-section of every part, sintering the powder along its path. The beam moves at hundreds of millimeters per second, but it still has to visit every contour on every layer. That is the core speed penalty. MJF fuses an entire layer in one lamp pass, which is why a tall bed of parts finishes faster.

Both leave the part inside a powder cake. Cooling is slow and controlled, often several hours, because a fast cool pulls the part and warps it. You then break the cake out, bead blast the surface and, if needed, dye or seal it.

The practical result: MJF and SLS produce similar-looking grey nylon parts, but MJF reaches a full build faster and SLS puts more energy into a smaller spot. That single difference explains most of the strength, detail and cost gaps below.

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  MJFAgent + infrared lamp fuses a whole layer at once
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  SLSLaser sinters one contour at a time
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  SharedNylon powder bed, slow controlled cooling, bead blast after

Strength in powder bed fusion is mostly about how well adjacent layers bond. MJF melts the powder more completely because the fusing agent pulls heat deep into the layer, so the bond between layers is close to the bond inside a layer. Test bars from MJF typically show near-isotropic behavior: tensile strength in Z is often around 90% of the XY value.

SLS can match that, but it depends on machine settings. Laser power, scan speed, hatch spacing and chamber temperature all move the result. A well-tuned SLS build gives isotropic parts with excellent fatigue life. A poorly tuned one shows layer delamination under load, especially on tall parts where the powder bed cools unevenly.

If your part sees impact, snap-fits or repeated flexing, MJF usually has the edge because elongation at break tends to run higher. If your part sees continuous static load and you control the build parameters, SLS is a solid choice. Neither process is the right answer for a part that must hold ±0.005 mm across a long span.

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  Pick MJFImpact, snap-fits, living hinges, Z-loaded brackets
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  Pick SLSStatic loaded parts with validated build parameters
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  Avoid bothTight tolerance metal interfaces, high-temperature service

MJF is faster on the machine. A single infrared pass fuses each layer across the full build area, so adding more parts to the bed barely changes the build time. Pack forty brackets into an MJF bed and the build still finishes in roughly the same window as one bracket. That is why MJF pricing drops steeply as quantity rises.

SLS build time scales with laser travel. More parts means more contours, and more contours means more time. The gap is small at one part and large at two hundred. For a single prototype, SLS and MJF often ship in the same week. For a 500-piece bridge run, MJF is usually the faster route.

Cooling and post-processing eat a fixed slice of the schedule for both. Powder cake cool-down, depowdering, bead blasting and any dyeing add hours regardless of process. When you plan a deadline, count those steps, not just the build.

At GreatLight we run 3D printing alongside 127 high-precision CNC machines, so a printed prototype can move straight into a machined version of the same geometry without a second supplier.

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  MJFBuild time nearly flat as part count rises
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  SLSBuild time grows with part count and height
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  BothAdd hours for cooling, depowdering and finishing

As-built MJF parts feel like fine sandpaper. Powder grains fuse at the surface and leave a uniform texture, typically in the Ra 8–12 μm range before blasting. Bead blasting brings that down and gives an even matte grey. You can dye MJF parts black, and because the process uses a fusing agent and colorants, grey, white and some colors are available.

SLS parts come out smoother straight from the cake. Laser sintering leaves a finer grain, often Ra 6–10 μm, and thin walls down to about 0.5 mm hold their shape well. Slots, small holes and fine lettering reproduce more cleanly because the laser spot is small and does not bleed sideways the way a fusing agent can.

Neither process gives you a machined finish. If a mating face needs Ra 0.8–1.6 μm or a flatness callout, plan a secondary machining pass. Printed bosses, bores and seal faces almost always need reaming or facing after printing.

A workable rule: choose SLS when the feature is the point, choose MJF when the quantity and color are the point.

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  MJFEven matte texture, dyeable, color options
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  SLSSmoother as-built, finer thin walls and slots
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  Secondary opMachine any sealing or bearing surface after printing

At one to five parts, the two processes land close together. Setup, powder handling and post-processing dominate, and the machine time difference is small. Expect quotes within a similar band, and pick on strength or detail instead of price.

Past roughly fifty units, MJF pulls ahead. Because a full bed fuses in one pass, the machine cost spreads across every part in that bed. SLS keeps paying for laser time per part. By a few hundred pieces, the gap is wide enough to change the sourcing decision on its own.

Material matters too. Both use nylon PA12 and PA11, and glass-filled or flame-retardant grades change the numbers. Specialty powders can swing cost more than the process choice does, so ask for a quote on the exact grade before you commit.

There is no minimum order quantity at GreatLight. A single prototype and a 10,000+ piece run go through the same quoting path, and you get a quotation with free DFM analysis within 12 hours.

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  1-5 partsQuote both, decide on strength or detail
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  50+ partsMJF usually wins on unit price
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  Any volumeConfirm the exact nylon grade before quoting

Choose MJF when you need many identical parts fast and the geometry is forgiving. Enclosures, brackets, jigs, ducting, covers and snap-fit housings all suit it. The near-isotropic strength and higher elongation handle clips and press-fits without cracking. Color and dyeing options help when the part is seen by a customer.

Choose SLS when the part itself is the hard part. Thin-walled ducts, small lattices, fine text, internal channels and tight feature spacing come out cleaner. It is also the safer pick for a one-off functional prototype where you want the smoothest as-built surface and you control the build parameters.

Skip both when the part needs metal-like stiffness, tight tolerances or high-temperature service. Nylon creeps under sustained load, absorbs moisture, and softens well below the temperatures an engine bay or a sterilization cycle will reach. For those parts, machined aluminium, stainless or titanium is the honest answer.

A common path with our customers: print the first article in MJF or SLS to check fit and assembly, then move to 5-axis CNC machining for the production version. The printed part validates the design; the machined part holds ±0.005 mm and the surface finish the drawing calls for.

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  MJFVolume, impact resistance, color, fast turnaround
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  SLSFine features, thin walls, smoothest as-built surface
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  NeitherTight tolerance, high temperature, metal-level stiffness