Choose SLS over FDM as soon as you need functional, isotropic end-use parts, designs with overhangs or complex internal structures, or production runs of 10 to thousands of parts. FDM remains useful for low-cost concept models; SLS is the production-grade choice for industrial PA12, PA11 and fibre-reinforced variants.
What SLS does that FDM cannot
The key structural difference: SLS builds parts by steering a laser through a powder bed. The unsintered powder around the part acts as built-in support, enabling overhangs, cavities and internal channels without support structures. FDM extrudes molten filament layer by layer and needs support above 45° overhangs which must later be removed.
Result: SLS parts are isotropic — strength is comparable in every direction. FDM prints have 30-50% anisotropy, with weak interlayer adhesion. For parts loaded in multiple directions, or that aren’t predictably oriented in use, that’s decisive.
SLS also scales efficiently: the build fills with dozens or hundreds of parts at once. FDM prints one part per machine per cycle. For runs above 10-20 parts, SLS is economically faster than FDM.
When FDM is still the right choice
FDM remains the cheapest option for:
- Concept models where look matters but mechanical strength doesn’t
- Large hollow parts where you can save heavily on material
- Applications where standard FDM colours (PLA, ABS, PETG) suffice
- In-house prototyping where you have your own desktop printer
For functional end-use products in PA12, PA11, fibre-reinforced materials or food-safe variants, SLS is the answer. FDM cannot deliver that material range in production-grade quality.
Which materials work for SLS at Parts on Demand?
We run 7 polymers across 11 industrial machines:
- PA12 (PA2200) — standard, 45 MPa, isotropic, smooth surface
- PA 950 HD — structurally black, 47 MPa, 35% lower cost for production runs
- PA11 — bio-based, 54 MPa, 31% elongation (tougher)
- PA12 Blue MD — food-safe (EC1935/2004 + FDA), metal-detectable, 49 MPa
- PA802CF — carbon-fibre reinforced PA11, 89 MPa
- Carbon LW (PA640GSL) — glass+carbon reinforced, 56 MPa, 2x stiffer than PA12
- TPU — flexible, Shore 88A, for seals and flex components
For tailored advice: upload your STEP file and our engineers compare strength, stiffness and cost-per-part for your specific application.