SLS printing, or selective laser sintering, is a 3D printing technology that uses a laser to fuse powdered material, typically nylon, into solid parts layer by layer. Unlike most other 3D printing methods, SLS doesn’t need support structures during printing, which makes it uniquely suited for complex geometries and functional parts. It’s one of the oldest and most established additive manufacturing technologies, widely used across aerospace, automotive, medical, and consumer product industries.
How the SLS Process Works
SLS builds parts inside a heated chamber filled with fine polymer powder. The process follows four repeating steps: the build platform lowers by one layer thickness, a recoating blade spreads a fresh layer of powder across the surface, the chamber heats the powder to just below its melting point, and then a laser selectively traces the cross-section of the part, fusing the powder particles together. This cycle repeats, layer by layer, until the entire part is complete.
Because the unsintered powder surrounding each layer acts as natural support, SLS can produce interlocking parts, internal channels, lattice structures, and other geometries that would be impossible or extremely difficult with other methods. You don’t need to design breakaway supports or worry about overhangs. The part simply sits in a “cake” of loose powder until printing finishes.
Standard layer thickness is 100 microns (0.1 mm), though machines can operate between 60 and 120 microns depending on whether you prioritize detail or speed. Dimensional accuracy typically falls within ±0.3%, with a minimum tolerance of ±0.3 mm. These specifications put SLS in a range that’s suitable for functional prototypes and end-use production parts, not just visual models.
What Happens After Printing
Once the laser finishes its final pass, the build chamber needs to cool to room temperature before you can handle the parts. This cooldown period prevents warping and can take several hours depending on the size of the build. Rushing this step risks distorting your parts.
After cooling, the solid block of powder (called the powder cake) goes to a depowdering station. Vibration shakes loose the unsintered powder, and you extract parts by hand using brushes and tools. A final sandblasting step clears powder from small holes, crevices, and fine features. For parts where a smooth surface finish matters, orienting those surfaces downward during the print setup produces cleaner results, while upward-facing surfaces come out crisper and sharper.
One of the practical advantages of SLS is powder recyclability. The unsintered powder from each build gets collected, sieved, and mixed with fresh powder for the next run. A common refresh ratio is 70% recycled powder to 30% virgin powder. Research on nylon 12 powder across seven consecutive print cycles at this ratio showed only a modest 4.5°C increase in melting temperature, meaning the material stays usable through multiple builds with minimal degradation.
Materials Used in SLS
Nylon is the dominant material family for SLS. The two most common grades are PA 12 (nylon 12) and PA 11 (nylon 11), both recognized for their robustness, durability, and resistance to wear. PA 12 is the most widely used SLS material overall, while PA 11 offers some distinct advantages for demanding applications.
PA 11 stands out for its elongation at break of around 30% and tensile strength reaching 45 MPa (roughly 6,500 psi). Its heat deflection temperature can reach 177°C (351°F), making it a strong candidate for parts exposed to high temperatures. PA 11 also resists a broad range of chemicals including hydrocarbons, fuels, alcohols, oils, and detergents. Perhaps most notably, PA 11 parts exhibit isotropic mechanical properties, meaning they have similar strength in all three build directions. This is unusual in 3D printing, where parts are often weaker along the vertical axis.
Beyond nylon, SLS machines can also process flexible thermoplastics like TPU for parts that need rubber-like elasticity, as well as glass-filled nylon composites for added stiffness and thermal resistance.
How SLS Compares to FDM and SLA
The three most common polymer 3D printing technologies are FDM (fused deposition modeling), SLA (stereolithography), and SLS. Each has a clear sweet spot.
- FDM melts and extrudes plastic filament through a nozzle. It’s the most affordable and accessible option, but parts show visible layer lines (0.1 to 0.3 mm layers) and are weakest in the vertical build direction. Tensile strength reaches roughly two-thirds of what injection molding achieves in the same material. FDM requires support structures for overhangs.
- SLA cures liquid resin with a UV laser or projector, producing the finest surface finish of the three (0.05 to 0.15 mm layers) with excellent detail and optical clarity. However, SLA parts tend to be brittle, have limited thermal performance, and are also weakest along the vertical axis. Support structures are required.
- SLS produces layers between 0.06 and 0.15 mm thick, with surfaces smooth enough that individual layers are hard to notice. Parts are durable, impact-resistant, and thermally stable. No support structures are needed. The tradeoff: SLS parts have a slightly grainy texture compared to SLA’s gloss, and print times run longer for large objects.
The core distinction is functional versus visual. If you need a part that looks polished for a presentation, SLA is the better choice. If you need a part that will be handled, loaded, snapped together, or exposed to heat, SLS wins. FDM occupies the budget-friendly middle ground for simpler geometries.
What SLS Parts Are Used For
SLS shines in applications where parts need to perform, not just look good. In aerospace, it produces lightweight ducting, brackets, and interior aircraft components. Automotive companies use it for functional prototypes that can withstand real-world mechanical testing, as well as small-batch production parts. The ability to print complex internal geometries without support structures makes SLS particularly valuable for airflow channels and custom housings.
In healthcare, SLS enables custom orthotics, prosthetic sockets, and surgical guides tailored to individual patients. The technology’s precision and material durability make it practical for devices that need to bear loads and resist repeated use. Dental applications benefit from the same customization, producing patient-specific tools and models.
Consumer products, sporting goods, and electronics enclosures are also common SLS outputs. Because the process doesn’t require molds or tooling, it’s cost-effective for production runs ranging from one part to several thousand, filling the gap between prototyping and full-scale injection molding.
Cost of SLS Printers
SLS equipment spans a wide price range. DIY and entry-level desktop SLS printers start around $10,000, though capabilities and reliability vary significantly at this tier. Benchtop industrial systems like the Formlabs Fuse 1+ 30W start at roughly $29,000, delivering part quality comparable to much larger machines. Traditional industrial SLS printers from manufacturers like EOS range from $200,000 to over $500,000, with the premium going toward larger build volumes, faster throughput, and multi-material capabilities.
Material costs also factor in. Nylon powder typically runs between $50 and $100 per kilogram depending on the grade, but the ability to recycle 70% of unused powder from each build significantly reduces waste and ongoing material expenses compared to processes where unused material is discarded.