SLS (Selective Laser Sintering) and MJF (Multi Jet Fusion) are both powder-bed nylon printing technologies that produce strong, functional parts without supports. They're often listed alongside each other on service bureau websites, and it's not always obvious which to choose. This guide breaks down the real differences — strength, surface quality, cost, color options, and which technology wins for specific applications.
How Each Technology Works
SLS — Selective Laser Sintering
SLS uses a high-power CO₂ laser to selectively fuse nylon powder particles layer by layer. The unfused powder surrounding each part acts as a natural support structure — no support material is needed. After printing, the entire powder bed cools slowly before parts are excavated, cleaned, and post-processed.
SLS was developed in the 1980s and has decades of industrial use. It's offered by a wide network of service bureaus worldwide.
MJF — Multi Jet Fusion (HP)
MJF, developed by HP and commercialized in 2016, uses an inkjet array to selectively deposit fusing and detailing agents across the powder bed, then passes an infrared heating element to fuse the treated areas. The process is fundamentally different from SLS but produces similar nylon parts.
MJF is faster than SLS for full build volumes and produces parts with slightly different mechanical and cosmetic characteristics.
Strength and Mechanical Properties
Both technologies produce nylon PA12 parts with excellent mechanical properties — far stronger than FDM and with more consistent isotropy (similar strength in all directions, unlike FDM's layer-direction weakness).
| Property | SLS (PA12) | MJF (PA12) |
|---|---|---|
| Tensile Strength | ~48 MPa | ~48 MPa |
| Elongation at Break | ~18% | ~20% |
| Isotropy | Good (slight Z weakness) | Very good (near-isotropic) |
| Density | ~0.93 g/cm³ | ~1.01 g/cm³ (slightly denser) |
Winner: Slight edge to MJF for isotropy and density. For most functional applications, both are equivalent — the difference is marginal unless you're engineering for exact mechanical specifications.
Surface Finish
Raw (as-printed) surface finish is where these technologies differ most noticeably to the eye and hand:
- SLS raw finish: Matte, slightly grainy, with a characteristic "sandstone" texture. White or light grey in color. Accepts paint and dye well after sanding.
- MJF raw finish: Darker grey to near-black (due to the fusing agent), slightly smoother than SLS. More uniform texture. The darker color can be an advantage or disadvantage depending on your application.
Both benefit from post-processing. Media blasting (glass bead or aluminum oxide) smooths the surface and gives a more professional look. Vapor smoothing (acetone or chemical) can produce near-injection-molded surface quality on both.
Raw SLS parts are white/light grey — easy to dye any color. Raw MJF parts are dark grey — dyeing lighter colors is difficult. If you need a specific color other than black or dark grey, SLS is easier to work with for dyeing. Both can be painted after priming.
Speed and Lead Time
MJF is significantly faster than SLS for equivalent part volumes. HP's MJF machines can process a full build volume in 3–4 hours vs. SLS's 10–20+ hours for an equivalent volume. This translates to shorter lead times at MJF shops — many offer 2–3 day turnaround vs. SLS's typical 3–5 days.
For high-volume production runs where you need to fill the entire build volume with parts, MJF's speed advantage is most pronounced. For single parts or small batches, both technologies offer similar turnaround times at most service bureaus.
Cost
For single parts and small batches: MJF is typically 10–20% cheaper than SLS for equivalent parts, driven by faster cycle times and higher machine throughput. The price difference narrows as batch size increases.
For large production runs filling the build volume: MJF wins on cost due to speed. More cycles per day = lower cost per part at volume.
You need white/light-colored parts, specialty SLS materials, or your service bureau only offers SLS
You want faster lead times, slightly better isotropy, or lower cost on production volumes
Material Options
SLS has been around longer and supports a wider material range:
- SLS materials: PA12, PA11, PA12-GB (glass-bead filled), PA12-CF (carbon fiber), TPU, PEEK, and specialty powders from various manufacturers.
- MJF materials: PA12, PA11, PA12-GB, TPU, and HP's own specialty materials. The material library is growing but still narrower than SLS.
If you need carbon fiber reinforced nylon, PEEK, or more exotic SLS powders, SLS is your only option — MJF doesn't support these yet.
Which Should You Choose?
For most functional nylon parts, MJF is the better default choice: it's faster, slightly cheaper, mechanically equivalent, and widely available. The main reasons to prefer SLS:
- You need white or light-colored finished parts (SLS raw color is easier to dye)
- You need specialty materials only available in SLS (PEEK, carbon-fiber nylon, etc.)
- Your local service bureau only offers SLS
- Your part has existing qualification on SLS and you can't change technology
Frequently Asked Questions
Marginally, in some properties. MJF PA12 is slightly more isotropic (uniform strength in all directions) and slightly denser than SLS PA12. For most engineering applications the difference is not significant — both produce excellent functional nylon parts. If you're designing to exact mechanical specs, request material data sheets from your service bureau and compare directly.
MJF uses a carbon-black fusing agent that gives raw parts a dark grey to near-black color. This is inherent to the process. If you need white or light-colored parts, specify dyeing or painting as post-processing, or consider SLS which produces naturally white/grey parts easier to dye.
Yes, through post-processing. SLS parts can be dyed a wide range of colors (the white base accepts dye well). MJF parts can be dyed dark colors (black, navy, dark red) but not lighter colors effectively. Both can be painted after primer application for any color.
No — this is one of the major advantages of both powder-bed technologies. The surrounding unfused powder supports the part during printing. This means you can print complex geometries, internal channels, moving assemblies, and interlocking parts that would require extensive supports in FDM or SLA.
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