The naming trap: not all laser 3D printing is metal
Both SLS and SLM sit under the powder-bed fusion family and both use a laser to build parts layer by layer from a bed of loose powder, which is why buyers often assume they print the same kind of part. They do not.
SLS fuses plastic powder, so the result is a tough polymer component. SLM fully melts metal powder, so the result is a genuine metal part. Confusing the two leads to wrong quotes, wrong lead times, and wrong expectations about strength, so the distinction matters from the first conversation.
How SLS works: sintering polymer powder
Selective Laser Sintering spreads a thin layer of polymer powder, usually nylon PA11 or PA12, across the build area and uses a CO2 or fiber laser to fuse the cross-section without raising the grains to full melt.
Unsintered powder supports the part as it grows, so SLS needs no support structures, and the surrounding powder is recycled for the next build. The finished part is a solid, lightly porous nylon component with good impact and chemical resistance.
How SLM/DMLS works: melting metal powder
Selective Laser Melting, also called DMLS, spreads a thin layer of metal powder such as stainless steel, titanium, or aluminum and uses a high-power fiber laser to fully melt that layer into a liquid pool that solidifies as dense metal.
Because the metal is truly melted, each layer fuses into a fully dense, near-wrought structure. Supports are usually required to manage heat and overhangs, and the part emerges from a mass of loose powder that is then removed and recycled.
Material families and what you can print
SLS runs on engineering polymers: unfilled and glass-filled nylon, TPU for flexibility, and specialty composites. These give you lightweight, insulating, and corrosion-proof parts that are easy to post-process.
SLM runs on real metal alloys: stainless steels, tool steels, titanium, aluminum, and nickel-based superalloys. That unlocks parts that conduct, dissipate heat, survive fire, and carry structural loads that no polymer could.
Strength, density and anisotropy
SLS nylon is strong for a plastic, with good fatigue resistance, but it is still a polymer: it softens with heat and will not carry metal-level loads. Properties can vary slightly with build orientation.
SLM parts are effectively solid metal with mechanical properties close to wrought material, though they too show some anisotropy between vertically and horizontally built directions. For load-bearing, high-temperature, or conductive applications, only SLM qualifies.
Dimensional accuracy and tolerances
SLS holds typical tolerances around +/-0.3 mm on small parts, limited by powder granularity and slight shrinkage as the nylon cools. It is excellent for fit and function but not for press-fit precision.
SLM holds tighter tolerances, often around +/-0.1 to +/-0.2 mm, because the melted metal solidifies in a well-controlled layer. Threaded features and bearing seats can be achieved, though critical dimensions are often finished by CNC after printing.
Surface finish and post-processing
SLS parts have a characteristic grainy, matte surface from the powder. They are commonly dyed, bead-blasted, or vapor-smoothed, and the finish is good enough for most enclosures and handles.
SLM parts come off the machine rough and may need stress relieving, support removal, and CNC machining of datums and holes. Surface can be improved by bead blasting or polishing, but metal post-processing is more involved and costly than polymer finishing.
Cost, lead time and build volume
SLS is relatively economical: the polymer powder is cheap, machines are widespread, and a batch of parts shares one build. It is the default for plastic prototypes and low-volume functional parts.
SLM costs more per part because metal powder, high-power lasers, and inert-gas atmospheres are expensive, and builds are slower. It pays off when machining the same geometry would waste material or be impossible, typically at low to mid volumes.
When SLS is the better choice
Choose SLS when the part is plastic and needs durability, complexity, or a small batch without any tooling. Ductwork, enclosures, jigs, and living-hinge parts are natural SLS applications.
SLS is also ideal when you want dozens of identical functional parts fast and cheap, or when the geometry has internal channels and snap features that would be hard to machine. If metal is not required, SLS is usually the smarter spend.
When SLM metal printing is the better choice
Choose SLM when the application demands real metal: structural brackets, heat exchangers, manifolds, surgical instruments, and lightweight lattice parts that must survive load and temperature.
SLM also wins for consolidation, merging several machined components into one printed assembly, and for low-volume production of complex metal parts where traditional machining would be slow or wasteful. Compare it against CNC before committing, since simple metal shapes are often cheaper machined.
How FabProto supports both
FabProto runs SLS for your polymer parts and partners with qualified SLM/DMLS metal printing for production-grade metal components, so you get one accountable source for both additive routes.
Our engineers help you decide whether a part belongs in nylon or metal, and whether SLM or CNC machining is the lower-risk, lower-cost path for your geometry and volume. That guidance keeps your additive program focused on parts that truly benefit from 3D printing.