What Is an SLS (Selective Laser Sintering)?

Selective laser sintering (SLS) is a powder bed fusion 3D printing process in which a laser fuses thin layers of polymer powder, most often nylon (PA12), into a solid part. The unfused powder around the part supports it during the build, so SLS needs no support structures and can produce complex, functional nylon parts.

In short: SLS is the go-to 3D printing process for tough nylon parts with geometry that would be hard to support or mold.

How Does Selective Laser Sintering Work?

A roller spreads a thin layer of powder across the build platform. A laser then scans the cross-section of the part and, in the words of Carl Deckard's original patent, is "switched on to sinter only the powder within the boundaries of the cross-section." The platform drops, a fresh layer of powder is spread, and the cycle repeats until the part is complete. The un-sintered powder is then removed and the part is lifted out.

Deckard developed the process at the University of Texas, and the patent was filed in 1986 and granted in 1989. It named plastic, metal and ceramic powders. Today "SLS" usually means polymer parts, and laser fusion of metal powder goes by names such as DMLS and SLM.

Preheating the powder bed lowers the temperature difference between the sintered and loose powder, which reduces thermal stress and distortion. Under ISO/ASTM 52900, SLS belongs to the powder bed fusion category. Multi Jet Fusion (MJF) and metal laser processes are in the same category.

SLS Materials and What They Are For

Material	Key properties	Typical applications
PA12 nylon	Good strength, low moisture absorption	Functional parts, snap fits, complex geometries
PA11 nylon	More impact resistant and ductile than PA12	Hinges, flexible functional parts
Glass-filled nylon (PA12-GF)	Higher stiffness, improved heat resistance	Structural brackets, stiffened components
Carbon-filled nylon (PA12-CF)	High stiffness, low friction, lightweight	Load-bearing parts, wear components
TPU	Flexible, abrasion resistant, rubber-like	Seals, gaskets, flexible joints

PA12 is the most widely used SLS powder. The material properties above are taken from NICE Rapid's SLS range.

When to Choose SLS

• Functional prototypes and end-use parts. SLS nylon suits assemblies, snap fits and living hinges that would crack in brittle resin.
• Geometry that is hard to support. Because the loose powder holds the part, internal channels, interlocking parts and organic shapes need no support removal.
• Surface finish is not the priority. SLS parts come out with a slightly rough surface. Sanding, priming, painting or dyeing improves the look, but for cosmetic models, SLA is the better starting point.
• Tolerances of about ±0.2 mm are acceptable. NICE Rapid holds SLS parts to ±0.2 mm (±0.008 in) with 100–180 µm layers. Tighter fits usually call for SLA, CNC machining or molding.
• Expect some porosity and direction-dependent strength. Both are listed limitations of powder bed fusion, so orient critical load paths with your supplier.

NICE Rapid runs SLS 3D printing in-house with a 2–3 day lead time and no minimum order.

Frequently Asked Questions

What is SLS 3D printing?

SLS 3D printing is a powder bed fusion process in which a laser sinters thin layers of polymer powder, usually nylon, into a solid part. Loose powder supports the part as it builds, so no support structures are needed and parts can be tough and functional.

What does SLS stand for?

SLS stands for selective laser sintering. The name describes the process: a laser selectively sinters only the powder inside each cross-section of the part, layer by layer, while the rest of the powder stays loose.

Does SLS need support structures?

No. The unfused powder surrounding the part supports overhangs and internal features during the build, then is removed afterward. This is one of the main differences from SLA and FDM, which both need supports.

Related Services at NICE Rapid

• 3D Printing — in-house SLS in PA12, PA11, glass-filled and carbon-filled PA12 and TPU, with ±0.2 mm tolerance and optional dyeing.
• Rapid Prototyping — SLS alongside CNC machining and vacuum casting, with engineers recommending the best process for each part.
• Request a Quote — upload an STL or STEP file and our team will confirm the process and lead time within 24 hours.

Sources

1. US Patent 4,863,538 (C. R. Deckard; assignee University of Texas System), Method and apparatus for producing parts by selective sintering (filed 1986, published 1989) — laser "switched on to sinter only the powder within the boundaries of the cross-section"; powder may be plastic, metal, ceramic or polymer — patents.google.com
2. Kafle et al., "3D/4D Printing of Polymers: Fused Deposition Modelling (FDM), Selective Laser Sintering (SLS), and Stereolithography (SLA)," Polymers — un-sintered powder removed after the build; preheating reduces the temperature gradient, thermal stress and distortion; PA12 is the most widely used SLS powder; SLS needs no support structures but has a rough surface finish — pmc.ncbi.nlm.nih.gov
3. Koltsaki et al., "A Comprehensive Overview of Additive Manufacturing Processes Through a Time-Based Classification Model," 3D Printing and Additive Manufacturing — ISO/ASTM 52900 powder bed fusion category includes SLS, SLM, DMLS and MJF; "no support requirement" as an advantage and "high porosity" and "anisotropy" as limitations — pmc.ncbi.nlm.nih.gov