For a functional nylon part, SLS wins on strength and watertightness while FDM wins on unit cost at low volume. SLS produces near-isotropic PA12 parts with no weak Z-axis and no leak-prone layer lines, whereas FDM nylon is anisotropic and porous along the build direction. At Layer X, we quote SLS nylon from ₹1,200 per part and FDM from ₹400 per part — so the honest answer depends on your load case, whether the part must hold pressure, and how many you need. This guide takes one nylon geometry, prints it both ways, and compares the two processes on the metrics that actually decide the job.
Why compare SLS and FDM on nylon specifically
Most process guides pit FDM against SLS in the abstract. That is not a fair fight, because they rarely run the same material. Nylon is the interesting case precisely because both processes can print it: our FDM service runs Nylon PA12 for fatigue-resistant, flexible snap fits, and our SLS service runs PA12 (Nylon 12) as its standard powder. Same polymer family, two completely different ways of turning it into a solid — one lays down molten filament layer by layer, the other fuses loose powder with a laser. Holding the material constant isolates what the process does to strength, finish and cost.
The part we use as our reference in this article is a mid-sized functional housing: roughly palm-sized, with internal ribs, a snap-fit lid, a cable-routing channel and two threaded bosses. It is the kind of geometry that separates the two processes cleanly, because it has features FDM struggles to support and SLS handles without a second thought.
Strength and isotropy: the Z-axis is the whole story
The single largest mechanical difference between the two processes is directional strength, or isotropy. FDM builds a part from stacked, bonded filament roads. Within a layer the polymer is continuous and strong; between layers, the bond relies on thermal fusion across the interface, and that Z-axis bond is weaker than the in-plane strength. Load an FDM nylon part across its layers and it will fail at a layer boundary well before the bulk material yields. This is anisotropy, and it is inherent to material extrusion — the ISO/ASTM 52900 additive-manufacturing terminology standard classifies FDM as "material extrusion" precisely because of this deposited, layered structure.
SLS is powder bed fusion. The laser sinters PA12 powder particle-to-particle in every direction, and because there is no distinction between "along a road" and "across a layer," the resulting part is close to isotropic — its mechanical properties are far more consistent regardless of load direction. That is why our SLS specification lists strength simply as Isotropic. For a snap-fit lid that flexes thousands of times, or a bracket that sees off-axis load, this is not a nicety; it is the difference between a part that survives and one that cracks along a layer line.
If you want to verify supplier claims independently, tensile properties of both processes should be reported against ISO 527 (tensile testing of plastics) with the specimen build orientation stated — an FDM data sheet that quotes only the strong in-plane number is telling you half the truth.
Watertightness and porosity
FDM parts are, by construction, porous. The stacked-road structure leaves microscopic voids at layer boundaries and between adjacent roads, so an FDM nylon part will typically weep or seep under pressure unless it is deliberately sealed, over-extruded, or printed with many solid perimeters. For a part that must hold air, water, or oil, this is a genuine limitation. We cover the sealing options in detail in our guide to achieving watertight 3D prints.
SLS nylon is fundamentally denser and more homogeneous because the powder fuses in all directions with no deliberate air gaps. Well-processed PA12 from SLS is close to watertight out of the machine and can be made fully sealed with a light infiltration or coating step. For fluid housings, pneumatic manifolds and enclosures with an IP-rated intent, SLS is the natural choice.
Surface finish and detail
The two processes finish very differently. FDM shows visible layer lines whose prominence scales with layer height, plus witness marks wherever support material touched the part. SLS produces a uniformly matte, slightly granular surface on every face — top, bottom and sides look the same because there are no supports at all. That consistency matters for consumer-facing parts and for any geometry where a support scar would land on a functional or cosmetic surface.
Geometry freedom follows from the same fact. SLS needs no support structures because the surrounding unsintered powder holds every overhang, so internal channels, captured hinges, trapped cavities and thin multi-direction walls all print freely. FDM must support overhangs beyond roughly 45°, and support removal from an internal channel is often impossible — which is exactly why our reference housing's internal rib-and-channel structure is straightforward in SLS and awkward in FDM.
Tolerance and material options side by side
Here is how the two Layer X nylon services compare on the specifications that go into a quote. Every figure below is our published process specification.
| Attribute | FDM (Nylon PA12) | SLS (PA12 Nylon) |
|---|---|---|
| Standard tolerance | ±0.3mm (±0.2mm process-qualified) | ±0.2mm |
| Strength / isotropy | Anisotropic — weaker Z-axis | Isotropic |
| Support structures | Required for overhangs | None — any geometry |
| Watertightness | Porous unless sealed | Dense, near-watertight |
| Build volume | 300 × 300 × 400 mm | Powder-bed nesting (batch) |
| Nylon material options | Nylon PA12 | PA12, PA12-GF, PA12-CF, TPU 88A/95A |
| Lead time | 3–5 days | 4–6 days |
| Price from | ₹400 per part | ₹1,200 per part |
Note the material breadth on the SLS side. Beyond standard PA12, our SLS nylon service offers glass-filled PA12-GF (higher stiffness and reduced creep for structural housings) and carbon-filled PA12-CF for the highest stiffness-to-weight — the latter being the route we take for lightweight brackets, as covered in our carbon-fibre 3D printing guide. FDM keeps a single unfilled PA12 grade.
Per-part cost at three volumes
Cost is where the decision usually turns, and it does not scale the same way for the two processes. FDM prices largely per part and per print hour — one machine prints one part (or a small plate) at a time. SLS prices around the powder bed: parts are nested three-dimensionally throughout the build volume, so the more parts you pack into a bed, the lower the effective cost per part. This gives the two processes different economic sweet spots.
- Prototype (1 part). FDM is the clear cost winner. A single functional nylon prototype starts from ₹400 per part on FDM versus from ₹1,200 per part on SLS, because a one-off cannot amortise an SLS bed. If the prototype only needs to prove fit and rough function, FDM PA12 is the economical call.
- Bridge batch (around 50 parts). The gap narrows. SLS nesting starts to earn its keep — fifty small housings share one bed and one machine cycle, so the SLS per-part figure drops toward its floor while FDM's stays roughly linear with quantity. Once you factor in FDM's support removal and any sealing labour on porous parts, a batch of 50 is where many nylon jobs cross over to SLS.
- Production run (around 500 parts). SLS is typically the lower total cost per functional part and the more consistent one. Dense bed nesting spreads the machine cost across hundreds of parts, and the isotropic, near-watertight result usually needs less remedial finishing. FDM remains viable for 500 simple parts, but for anything load-bearing or sealed, SLS wins on both cost-per-good-part and yield.
We do not publish fixed per-unit prices at each volume because nesting efficiency depends entirely on your specific geometry — a tall, hollow part nests differently from a flat plate. That is what the quote is for. Both services carry no minimum order quantity, so you can prototype on FDM and move the same file to SLS for production without re-engineering.
Which process should you choose?
Choose FDM nylon when the part is geometrically simple, the load is modest or single-direction, watertightness is not required, and you need one or a handful of units at the lowest cost. Choose SLS nylon when the part has internal channels or captured features, must take off-axis or cyclic load, needs to hold pressure or fluid, has to look consistent on every face, or is heading for a batch of tens to hundreds. For our reference housing — internal ribs, a flexing snap-fit lid and a sealed cable channel — SLS is the right process on strength, watertightness and finish, and it becomes the cheaper process too once quantities pass the prototype stage. If you are still weighing the broader process families, our FDM vs SLA vs SLS process guide sets out the full picture, and our FDM 3D printing service page details the wider polymer range.
Not sure which side your part lands on? Upload your CAD file for a 24-hour quote and our team will spec it both ways so you can compare strength, finish and cost directly — start your quote here.