Comparing SLS (Selective Laser Sintering) and MJF (Multi Jet Fusion) without talking about the specific powder you are using is like comparing two ovens without mentioning whether you are baking a cake or roasting a chicken. The machine matters, but the material dictates the final result.

While both technologies melt microscopic polymer powders to create parts, how those powders react to lasers (SLS) versus fusing agents and infrared lamps (MJF) changes dramatically depending on the chemical recipe.

If you are trying to decide whether to print your next batch of parts in PA12, PA11, PA6, TPU, or a fiber-filled composite(Nylon GF/CF), here is exactly what those parts will look and feel like when they land on your desk.

🎯 Key Takeaways

• PA12 & PA11: The workhorses. MJF provides slightly sharper edges and a denser feel, while SLS is capable of providing a chalky white baseline perfect for custom dyeing.
• PA6: The industrial heavyweight. Primarily found in high-end SLS machines, it offers unmatched thermal resistance but naturally prints with a rougher, more porous surface than PA12.
• TPU (Flexible): MJF TPU tends to be darker and denser, while SLS TPU is lighter, highly porous, and feels a bit like a stiff sponge before post-processing.
• The Composite Trade-Off: Adding glass or carbon fiber to any powder will drastically increase its strength, but it will ruin the smooth finish, giving the part the texture of fine sandpaper.

🛠️ The Standard Polyamides (Nylons)

PA12 (Nylon 12): The Industry Baseline

If you order a “Nylon” 3D print without specifying the exact chemistry, you are getting PA12. It is the most stable and popular powder on the market.

• SLS Surface Finish: Raw SLS PA12 comes out chalky white or gray. It has a distinctly matte, “sugary” texture. You can easily feel the microscopic porosity, but it acts like a blank canvas and absorbs colored dyes beautifully.
• MJF Surface Finish: Because MJF uses dark fusing agents to absorb heat, raw MJF PA12 comes out in a patchy “battleship gray.” It feels noticeably denser and slightly smoother than SLS. MJF also uses a detailing agent that prevents excess powder from melting, resulting in crisper edges and finer embossed text.
• The Verdict: MJF wins on raw detail and edge sharpness. SLS wins if you need your parts dyed in vibrant, custom brand colors.

PA11 (Nylon 11): The Ductile Sibling

PA11 is ecologically derived from castor oil and is much more flexible and impact-resistant than PA12. If you are printing living hinges or snap-fits, this is your powder.

• Surface Finish Comparison: Aesthetically, PA11 looks almost identical to PA12 in both technologies. However, because of its thermal properties, PA11 can sometimes exhibit slightly more “orange peel” texturing on large, flat surfaces compared to PA12. SLS PA11 is still highly dyeable, while MJF PA11 remains strictly in the gray/black color palette.

🏗️ The Heavy Hitters & Specialty Powders

PA6 (Nylon 6): The High-Temp Beast

PA6 is an incredibly stiff, high-temperature engineering thermoplastic. While HP (MJF) has introduced some PA6 blends, true PA6 is heavily dominated by industrial open-platform SLS machines (like those from Farsoon- And Primofort had it! ) because it requires extremely high and precise chamber temperatures to print successfully.

• Surface Finish Comparison: PA6 does not print as “prettily” as PA12. Because it requires higher melting temperatures and cools differently, the raw surface finish of an SLS PA6 part is noticeably rougher and more porous than standard nylons. It feels highly industrial.
• The Verdict: You don’t choose PA6 for its looks; you choose it because you need to bolt a part directly onto a hot car engine. Always plan to media-tumble (vibro-polish) PA6 parts to knock down the surface roughness.

TPU (Thermoplastic Polyurethane): The Rubber Band

Printing flexible rubber-like parts in a powder bed is a game-changer for gaskets, grips, and footwear.

• SLS Surface Finish: SLS TPU parts are naturally white or off-white. Straight out of the printer, they feel incredibly porous—almost like a dense, stiff sponge. Dirt and grease will instantly stick to raw SLS TPU.
• MJF Surface Finish: MJF TPU (often Ultrasint) prints in gray/black. It feels significantly less porous than the SLS version, behaving more like a dense vulcanized rubber.
• The Verdict: MJF generally provides a superior “out-of-the-box” tactile feel for flexible parts, as the darker color hides dirt and the denser fusing process feels more like traditional rubber. Both require chemical vapor smoothing if you want them to be watertight.

🪨 The Composites: Fiber-Filled Nylons

If standard nylon isn’t stiff enough, manufacturers mix additives into the powder. This is where surface finish takes a massive hit.

• Glass Fibers (SLS) vs. Glass Beads (MJF): SLS commonly uses PA12 GF (Glass Fiber), which involves microscopic shards of glass. MJF commonly uses PA12 GB (Glass Beads), which are microscopic spheres.
• Carbon Fiber (SLS/MJF): Chopped carbon fibers are added for ultimate stiffness and light weight.
• The Surface Finish Reality: No matter which technology you use, composites feel like sandpaper. Because the polymer matrix shrinks slightly as it cools, the microscopic glass or carbon fibers are left protruding just above the surface.
• The Verdict: If you are printing a sleek consumer product, avoid fiber-filled powders. If you must use them for structural reasons, they require aggressive post-processing (sanding, tumbling, or thick epoxy coatings) to achieve a smooth finish.

📊 The Material Surface Finish Summary Table

🚀 The Client-Oriented Verdict: Designing for the Finish

When you are ordering parts, you have to balance mechanical needs with visual expectations.

If you are prototyping a consumer electronics enclosure that needs to look gorgeous on a desk, stick to standard PA12 and request vapor smoothing. It will melt away the 0.1 mm0.1 mm (0.004 inch0.004 inch) layer lines and leave you with an injection-mold-like gloss.

If you need a rugged, grippy handle for a power tool, MJF TPU or a tumbled SLS PA11 part will provide excellent tactile feedback.

And remember: the moment you add glass or carbon fiber to your powder (PA12 GF/CF), you are sacrificing your smooth surface finish on the altar of mechanical strength. Choose your powders wisely, plan your post-processing, and your 3D prints will never look like “prototypes” again!