Characteristics of Nylon in 3D Printing

• 1
  What makes nylon different from other print plastics
• 2
  Moisture absorption and what it does to a printed part
• 3
  Layer bonding, anisotropy and load direction
• 4
  Chemical, thermal and wear behavior in service
• 5
  Choosing between printed and machined nylon parts
• 6
  When to print nylon and when to machine it

Nylon is a polyamide. The chain is held together by amide groups that hydrogen-bond to each other. Those bonds are the reason a nylon part bends instead of shattering, and they are also the reason the material pulls water out of the air. Every other property on this page follows from that one structural detail.

Compare it with PLA or PETG. Those polymers are stiff and easy to print because their chains barely move. Nylon chains slide. A printed nylon bracket can flex a few millimeters under load and return to shape. PLA would crack at the same deflection. That toughness is why nylon shows up in living hinges, clips and snap-fit housings.

The trade is process control. Nylon has a narrow window between a bed that grips and a bed that warps. It also absorbs moisture before and after printing. A sealed spool of PA12 can pick up 1–2 % water in a humid room over a few weeks. Wet filament foams at the nozzle and leaves porous layers.

Grades matter more than the word nylon. PA6 is stiffer and absorbs more water. PA12 absorbs less and prints with better dimensional stability. PA66 has a higher melting point and is harder to run on desktop hardware. Carbon-fiber and glass-filled grades raise stiffness and lower warp.

For an engineer, the practical question is not whether nylon is strong. It is whether your geometry, your machine and your humidity control can deliver the same part twice. That is a process question before it is a material question.

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  PA12Lowest moisture pickup, best dimensional stability, the default for SLS
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  PA6Higher strength and heat resistance, more warp and more drying
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  PA66High melting point, industrial machines only
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  Filled gradesCarbon or glass fiber cuts warp and raises stiffness

Polyamide absorbs water into the amorphous regions between crystals. The water acts like a plasticizer. A dry PA6 part is stiff and slightly brittle; the same part after conditioning is tougher and a little larger. Published saturation values for PA6 sit near 8–10 % by weight in boiling water, and around 2–3 % in normal indoor air. PA12 settles closer to 1–1.5 %.

In the printer this shows up as bubbles, a rough surface and weak layer adhesion. The nozzle heats water trapped inside the filament, the water turns to steam, and the extruded bead foams. You hear a popping sound. The fix is drying, not a temperature change: 70–80 °C for 4–6 hours for PA12, and 80 °C for 6–8 hours for PA6.

After printing, moisture keeps moving. A dry part grows as it conditions. A PA6 part can gain 0.2–0.5 % in linear dimension over days in a humid shop. A 100 mm hole may close by 0.3 mm. If the drawing has a tight bore, print it undersized and ream after conditioning, or design the fit around the conditioned size.

For parts that must hold tolerance, condition first and measure second. We see the same behavior in machined PA stock. Extruded nylon bar absorbs water on the shelf, and a shop that machines it dry will find the bore tight the following week. The material does not care which process shaped it.

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  Dry before printing70–80 °C for 4–6 hours, PA12
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  Longer for PA680 °C for 6–8 hours, then keep in a dry box
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  Allow conditioningLet the part sit 24–48 hours before final measurement
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  Tight boresPrint undersize and ream after the part stabilizes

FDM nylon is not one material. It is a stack of welded beads. Bond strength between layers depends on how hot the previous layer still is when the next one lands. Print a tensile bar flat and you measure the polymer. Print it upright and you measure the weld line. The gap is real: an upright FDM part can lose a large share of its strength across layers.

SLS behaves differently. The laser melts powder in place and the part is largely isotropic in the build plane, with a modest drop in the Z direction. That is why functional nylon prototypes usually go to SLS when load direction is unknown, and to FDM when the geometry is large and the load path is known.

Design around the grain. A printed clip should bend along the layer plane, not peel across it. Put the seam away from the highest stress. Add a fillet where the load enters the part; nylon tolerates flex but not a sharp corner acting as a crack starter.

Wall count beats infill percentage for strength. Three 0.4 mm walls carry more load than 60 % infill with two walls. If the part is a structural bracket, model it as a shell with ribs, then print the ribs along the load path.

Temperature matters here too. A hot chamber near 60–80 °C keeps the weld line open longer and raises Z strength. A cold shop with a draft will give you warped corners and a weak part, no matter what the spool label says.

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  FDMStrong in-plane, weaker across layers
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  SLSNear-isotropic in the build plane
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  Walls firstThree perimeters beat high infill for stiffness
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  Hot chamber60–80 °C improves weld strength

Nylon resists oils, greases, fuels and many solvents. It does not resist strong acids, phenols or long exposure to hot water. For automotive under-hood parts, the useful property is resistance to fuel and oil at moderate temperature, not universal chemical immunity. Check the specific fluid and the operating temperature together.

Heat deflection is where marketing numbers mislead. Unfilled PA6 may show an HDT near 60–70 °C at 1.8 MPa, and filled grades push higher. A printed part loses stiffness before it deforms visibly. A bracket that feels rigid at 23 °C can creep at 60 °C under the same load. If the service temperature is above 80 °C, look at PEEK or a machined metal part.

Wear behavior is good. Nylon has a low friction coefficient and handles sliding contact against steel, which is why it is common in gears, bushings and wear pads. Add carbon fiber and the wear rate drops further, though the part becomes more abrasive to whatever it rubs against.

UV is the weak point outdoors. Unstabilized nylon yellows and loses impact strength under sunlight. Black grades with UV stabilizers last longer but still age. For permanent outdoor duty, plan on a coating, a cover, or a different polymer.

Water is the quiet variable. A part submerged in water keeps absorbing until it saturates. Dimensions grow, stiffness drops, and the effect is reversible only if the part dries out completely. For wet service, design clearance for the saturated size.

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  Good resistanceOils, greases, fuels, many solvents
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  AvoidStrong acids, phenols, hot water long term
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  Wear partsGears, bushings, wear pads, low friction
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  OutdoorsUV stabilizer helps but does not stop aging

Use printing when the value is speed and geometry. A design that has not been frozen, a duct with a curved internal path, a run of five brackets for a test rig. SLS gives you a tough part in days without a mold, and the material behaves close to isotropic. That is a real advantage and it is hard to replace.

Switch to machining when the value is repeatability. A printed part is the sum of nozzle temperature, chamber temperature, layer time, humidity and machine calibration. Two printers in the same shop can differ. A CNC program cuts the same part from the same bar stock on Monday and on Friday. For a production run of 500 identical parts, that difference decides whether your assembly closes.

Nylon is available as extruded bar and plate in PA6, PA6 cast, PA12 and filled grades. We machine it on the same 3-axis and 5-axis centers used for aluminum, with sharp tooling, high spindle speed and air or coolant to clear chips. Nylon cuts cleanly but it melts if the tool rubs. Feed per tooth and chip clearance matter more than raw spindle speed.

Hybrid builds are common. Print the complex housing in SLS nylon, machine the mating face and bores, then assemble. The printed body carries the shape, the machined insert carries the tolerance. This keeps tooling cost near zero and still gives you a bore that measures the same on every unit.

If your part needs a flat sealing face, a press fit, a bearing bore or a thread that will be assembled thousands of times, machine it. If it needs to exist next week and the geometry is organic, print it first and validate the fit.

• 1
  Print firstUnfrozen design, complex internal paths, low volume
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  Machine for tolerancePress fits, bearing bores, sealing faces
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  HybridSLS body plus machined interface faces
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  Let us quote bothSend the model and we compare routes