Nylon PA12: Properties, SLS/MJF Powder & FDM Filament

Nylon is the family name for a class of polyamides, the same engineering polymers that injection molders have used for decades to make gears, bushings, cable ties, and under-hood components. In 3D printing, nylon matters because it is one of the few printable materials that genuinely behaves like a molded engineering plastic: it is strong, tough, abrasion-resistant, and able to flex and recover rather than crack. Where PLA is stiff but brittle and ABS is tough but not wear-resistant, nylon fills the role of a durable mechanical material that survives repeated use, impact, and rubbing contact.

The defining feature of printed nylon is that it spans two very different process families. As a powder, almost always PA12 or PA11, it is the workhorse material of SLS and MJF, where it produces strong, isotropic, support-free functional parts. As a filament, usually PA6 or PA12, it runs on FDM machines, where it is cheaper and more accessible but more moisture-sensitive and weaker across the layers. The choice between powder and filament, and between PA6 and PA12, is the central decision in any nylon project. Its tensile strength runs from 40 to 75 MPa and its elongation at break reaches 100 to 300 percent, so a nylon part bends and absorbs energy before it fails rather than snapping. The trade-offs are moisture sensitivity, moderate heat resistance, and, on FDM, anisotropy, and each one shapes how nylon is specified and used.

What nylon is, and why the grade matters

Nylon is a polyamide, meaning its polymer chains are linked by amide groups, and it is sold under several grade numbers that differ in the length of their carbon segments between those amide bonds. The two grades that matter most for 3D printing are PA12, with twelve carbons, and PA6, with six. That single structural difference drives nearly every practical choice between them. The longer segments in PA12 make the chains less polar and less attracted to water, so PA12 absorbs only about 1 percent moisture at equilibrium. The shorter segments in PA6 make it more polar and more hygroscopic, so PA6 absorbs about 9 percent. That nine-fold difference in moisture uptake is the reason PA12, not PA6, dominates powder-bed printing and any application where dimensional stability matters. PA11, made from castor oil rather than petroleum, sits close to PA12 but is tougher and more ductile, which makes it the preferred grade for parts that must flex repeatedly, such as living hinges.

The key point is that “nylon” is not one material but a family, and the grade is a design input. Specifying “nylon” without naming the grade, the process, and whether the part is filled leaves the most important variables undefined, so a clear nylon callout names all three.

Nylon material properties

Density, tensile strength, and elongation

Nylon PA12 has a density of about 1.02 grams per cubic centimeter, which is light for an engineering polymer, while PA6 is denser at about 1.14. Both are markedly lighter than metals, which is part of why printed nylon replaces aluminum in non-structural brackets and housings. The tensile strength of printed nylon runs from 40 to 75 MPa, with the lower end typical of as-printed SLS PA12 and the upper end reached by filled FDM grades, and the elongation at break stretches from 100 to 300 percent. That elongation is what sets nylon apart from stiffer, more brittle printed materials: a nylon part yields and deforms rather than fracturing, so it survives impacts and assembly forces that would crack PLA or a standard resin.

Heat deflection temperature

The heat deflection temperature runs about 55 to 65 degrees Celsius for PA12 and 65 to 80 degrees Celsius for PA6. This is serviceable for warm environments and brief thermal excursions, but it is below the roughly 95 degrees Celsius that ABS reaches, and well below the 200-plus degrees of PEEK or ULTEM. Nylon is therefore a room-temperature and warm-service material, not a high-temperature one, unless it is filled. Filled grades, discussed below, lift the heat deflection temperature meaningfully and extend nylon into hotter, more loaded duty.

Chemical resistance and moisture

Chemically, nylon resists oils, fuels, greases, and many common solvents, which is why it has a long history in automotive and machinery applications. Strong acids and some chlorinated solvents attack it, so nylon is not a universal chemical-resistant material, but for the hydrocarbon and lubricant exposures typical of mechanical assemblies it holds up well. Its moisture absorption, low for PA12 and high for PA6, is the one property that demands active management, because it changes both dimensions and mechanical behavior over the part’s life.

Powder versus filament: the central nylon choice

The most important decision in a nylon project is not the grade but the process, because powder and filament nylon behave like two different materials.

Powder nylon (SLS and MJF)

On SLS and MJF, a bed of PA12 powder is fused layer by layer, usually by a laser or a fusing agent and infrared energy, with no supports needed because the unfused powder supports the part. The result is a strong, largely isotropic part, because each layer is welded into a continuous solid rather than bonded as a separate bead. There is no Z-direction weakness to design around, which is why SLS and MJF PA12 is the default for functional, load-bearing nylon parts.

Filament nylon (FDM)

On FDM, nylon filament is extruded through a nozzle one track at a time, and each layer bonds to the one below as a warm bead. That bond is weaker than the material within a track, so an FDM nylon part is about 20 to 30 percent weaker along the Z, or build, direction than within the layer plane. For a part that takes load across the layers, that anisotropy is a real limit, and it must be designed around by orienting the part so the load runs along the layers. FDM nylon also needs a high nozzle temperature, a heated bed, and dry storage, because wet filament prints with bubbles, stringing, and weak layers.

Practical summary

The practical summary is that powder nylon is stronger, more isotropic, more dimensionally stable, and free of support-removal labor, while filament nylon is cheaper, faster for one-off parts, and accessible on a desktop machine. For a functional gear, a load-bearing bracket, or a part that must behave like an injection-molded component, SLS or MJF PA12 is almost always the right answer; for a quick prototype, jig, or non-critical part where the anisotropy can be designed around, FDM nylon is an economical choice.

PA6 versus PA12

Within each process, the choice between PA6 and PA12 comes down to strength versus stability. PA6 has higher tensile strength and stiffness, which makes it attractive for heavily loaded parts, but it absorbs about 9 percent moisture at equilibrium, which swells the polymer, shifts dimensions, and drops the glass transition temperature enough to soften the part in service. That moisture uptake also makes PA6 harder to print, because wet PA6 filament foams in the nozzle and produces porous, weak layers. PA12 trades a little of that strength for far better stability: it absorbs only about 1 percent moisture, so its dimensions and properties drift much less in humid service, and it processes cleanly on SLS, MJF, and FDM. For powder-bed printing, PA12 is essentially the only grade in widespread use, because its low moisture uptake and reliable sintering behavior make it the stable, repeatable choice.

PA6 retains a role where its extra strength is worth the stability penalty and where the part can be kept dry, such as in sealed assemblies or in filled grades where the filler carries much of the load. But for the majority of nylon applications, PA12 is the standard, and specifying it by name avoids the moisture-driven surprises that PA6 brings.

Strengths of printed nylon

Nylon’s strengths are strength, toughness, abrasion resistance, and wear resistance, and on powder processes, isotropy. It carries static load well, survives impact without shattering, and resists the rubbing and sliding contact that would quickly wear down a softer polymer. Its natural surface lubricity means nylon-on-nylon or nylon-on-metal sliding pairs run with less friction and less galling than many alternatives, which is why printed nylon gears, bushings, and bearings are common in functional assemblies. The toughness shows up most clearly in snap-fits and living hinges, where PLA and standard resins are too brittle and fail early while nylon’s high elongation lets it flex and recover.

The isotropy of powder PA12 is itself a strength worth naming separately. Because the fused layers are continuous solids rather than bonded beads, an SLS or MJF nylon part has nearly the same strength in the Z direction as in the layer plane. For a part that takes load from an unknown or varying direction, that isotropy is a decisive advantage over FDM, where the designer must always know where the load runs and orient the part to suit.

Limitations and how to manage them

Nylon’s limitations are moisture sensitivity, moderate heat resistance, and printing difficulty on FDM, and each one has a standard mitigation. Moisture is managed by choosing PA12 over PA6 where stability matters, by drying filament before printing, and by designing for the small dimensional drift that even PA12 shows in humid service. The moderate heat deflection temperature is managed by filling the nylon: glass- and carbon-fiber-filled grades raise stiffness, strength, and heat resistance, extending nylon into warmer, more loaded applications. Unfilled nylon should not be specified for sustained service above its heat deflection range.

The FDM difficulty is managed by process discipline: a high-temperature hot end, a heated bed, an enclosure for larger parts, and a sealed filament dryer or dry box. FDM nylon is one of the more demanding filaments and is not a beginner material, but on a capable machine it produces tough, functional parts at a fraction of the cost of SLS. The anisotropy remains and must always be designed around, because no amount of tuning removes the layer-bond weakness inherent to the process.

Filled nylons

Stiffness and heat-resistance gains

Glass-filled and carbon-filled nylons are the standard route to higher stiffness, strength, and heat resistance in a printed nylon part. The filler, typically short glass or carbon fibers chopped to a fraction of a millimeter, is mixed into the base polymer and carries a share of the load, which can roughly double the stiffness and lift the tensile strength toward the top of nylon’s range. Filled grades also warp less than unfilled nylon on FDM, because the fibers restrain shrinkage, which makes them easier to print large.

Trade-offs: surface, elongation, and tool wear

The trade-offs are a rougher as-built surface, lower elongation, and tool wear. The filler interrupts the polymer’s ductility, so a filled nylon part is stiffer but less tough than its unfilled counterpart, and it fails more abruptly. The as-built surface of a filled grade is noticeably rougher and more textured, which can matter for sliding contacts or cosmetic faces. And on FDM, carbon-filled nylon is abrasive enough to wear a standard brass nozzle quickly, so a hardened steel or ruby nozzle is required, and even then nozzle life is shorter than with unfilled filament.

A filled-nylon example

For example, a structural drone arm that must be light, stiff, and survive flight loads is a good fit for carbon-filled nylon on FDM, where the filler adds stiffness and reduces warping on a part that would be hard to print in unfilled nylon. The trade-off, a rougher surface and a more brittle failure mode, is acceptable because the arm is sized for stiffness, not for impact. Filling changes the material’s character as well as its numbers, so a filled grade is chosen when stiffness and heat resistance outweigh toughness and surface quality.

Applications and use cases

Nylon earns its place for durable mechanical and functional parts that must work like molded components. Gears, bearings, and bushings are classic applications, because nylon’s strength, wear resistance, and natural lubricity suit sliding, rotating duty. Brackets and mounts that carry static or cyclic load, snap-fits and living hinges that must flex repeatedly, cable ties and clips, and housings that resist impact and wear are all strong fits. Anywhere a part must survive real use rather than sit on a desk as a model, nylon is the natural material.

For example, a functional gear for a low-speed mechanism is printed in SLS PA12 because it must carry torque and resist wear without the anisotropy of an FDM print, and because the powder process needs no supports that would mark the teeth. The gear runs quieter and lasts longer than a PLA equivalent, which would wear quickly and crack under shock load. e.g., a snap-fit battery door that must open and close hundreds of times is printed in PA11 or PA12 nylon, because a living hinge in PLA or ABS would crack within a few cycles, while nylon flexes and survives the full service life. Other common uses include jigs and fixtures that must survive shop-floor handling, impellers and fans in warm air or fluid, and prototyped components that will later be injection-molded in the same nylon family, so the printed part approximates the molded one’s behavior.

Design rules for printed nylon

Designing for nylon means designing for its process and its moisture behavior.

On SLS and MJF

On SLS and MJF, design escape holes of 2 to 3mm in any hollow feature so unfused powder can drain, keep walls at least 0.8mm, and remember that the slightly grainy as-built surface may need smoothing for a sliding or sealing face. Large flat sections are fine on powder processes because there are no supports and no curl, which is one reason SLS nylon suits covers and housings that would warp on FDM.

On FDM

On FDM, orient the part so functional loads run along the layers, never across them, and treat the 20 to 30 percent Z-direction weakness as a hard design limit rather than a defect to ignore. Use a hardened nozzle for any filled grade, dry the filament before printing, and store it sealed with desiccant between builds. Add a brim or raft for larger parts to anchor the edges against warping, and prefer an enclosed, heated chamber for anything beyond small geometry.

Across both processes: moisture

Across both processes, dry nylon before printing and design for the moisture drift the part will see in service. For PA12 this is a small effect, on the order of a fraction of a percent in dimension, but for PA6 it can be several percent, which is enough to change a clearance fit. If the part must hold a tight fit over years of humidity cycling, specify PA12, design the tolerance around its drift, or plan to machine the critical face after printing.

Alternatives and when not to use nylon

Choose ABS when higher heat resistance, around 95 degrees Celsius, or acetone vapor smoothing matters more than wear resistance. Choose PETG for easier FDM printing and good toughness at moderate cost, accepting lower strength and lower heat resistance than nylon. For a fine-detail or cosmetic surface that nylon’s grainy powder or rough FDM layers cannot deliver, choose SLA, which wins on resolution and finish at the cost of toughness. For hot service above nylon’s range, choose a high-temperature resin or, for sustained structural duty, PEEK or ULTEM, which reach heat deflection temperatures above 200 degrees Celsius but require specialized machines and cost far more.

Do not use nylon when moisture stability is critical and the only available process is FDM PA6, when the part must run hot without a filled grade, or when a fine cosmetic surface is required and post-processing is not an option. In each of those cases a different material does the job better, and forcing nylon into it produces a part that disappoints in service.

Tolerances

Tolerance by process

On SLS and MJF, PA12 holds about plus or minus 0.2 to 0.5mm, strong and largely isotropic, with no support marks to clean up. On FDM, nylon runs looser, about plus or minus 0.3 to 0.5mm, and is both moisture-sensitive and anisotropic, so the achievable tolerance depends on how the part is oriented and how dry the filament stays. The best small SLS or MJF PA12 parts can reach the tight end of that range, while large or flat FDM nylon parts tend toward the loose end, especially where warping and moisture drift compound.

Precision fits and moisture drift

For a precision fit on a mating face, plan to machine or ream the critical surface after printing, because the as-built surface will not hold a tight clearance regardless of process. Remember that moisture uptake in service can slightly shift dimensions on PA6 and, to a lesser degree, on PA12, so a fit that is correct on a dry, freshly printed part may drift over time in a humid environment. Specifying PA12, designing the tolerance around its small drift, and machining critical faces after printing together produce a nylon part that holds its fit through real service.