What Is Selective Laser Sintering (SLS)?

DefinitionSelective 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.

Explained

How Does Selective Laser Sintering Work?

A roller spreads a thin layer of powder across the build platform. A laser scans the cross-section of the part and 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; the patent was filed in 1986 and granted in 1989. It named plastic, metal and ceramic powders. Today "SLS" usually means polymer parts, while laser fusion of metal powder is referred to as DMLS and SLM.

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

SLS Materials and What They Are For

PA12 is the most widely used SLS powder. Common materials include:

PA12 nylon — good strength, low moisture absorption; used for functional parts, snap fits and complex geometries.
PA11 nylon — more impact resistant and ductile than PA12; used for hinges and flexible functional parts.
Glass-filled nylon (PA12-GF) — higher stiffness, improved heat resistance; used for structural brackets and stiffened components.
Carbon-filled nylon (PA12-CF) — high stiffness, low friction, lightweight; used for load-bearing parts and wear components.
TPU — flexible, abrasion resistant, rubber-like; used for seals, gaskets and flexible joints.

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 loose powder holds the part, internal channels, interlocking parts and organic shapes need no support removal.
Surface finish is not the priority. SLS parts have a slightly rough surface; sanding, priming, painting or dyeing improves the look, but SLA is better for cosmetic models.
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 the team will confirm the process and lead time within 24 hours.

Key takeaways

SLS is a powder bed fusion 3D printing process that uses a laser to sinter polymer powder, most commonly PA12 nylon.
Unfused powder supports the part during printing, so SLS needs no dedicated support structures.
It is well suited to functional prototypes, snap fits, living hinges and complex geometries.
Common SLS materials include PA12, PA11, glass-filled PA12, carbon-filled PA12 and TPU.
SLS parts have a slightly rough surface, some porosity and direction-dependent strength; typical tolerance is about ±0.2 mm.
The technology was patented by Carl Deckard in 1986/1989 and is classified under ISO/ASTM 52900 powder bed fusion.

Example

An SLS PA12 bracket with internal channels and snap-fit features can be built without support structures because the surrounding powder holds the geometry, then dyed or painted for a functional prototype or end-use part.