People arrive at nylon looking for strength, which is a reasonable thing to look for and the wrong reason to choose it. PA6's tensile range of 50 to 80 MPa is genuinely above PETG's 45 to 55, but the gap is not what makes nylon worth its considerable trouble, and it is not what will decide whether your part works.
The decision is water. Nylon absorbs it from the air faster than anything else on this site, and it keeps absorbing it after the part is finished and installed.
Water before printing, and water afterwards
Two separate problems share one cause, and conflating them is why nylon advice sounds contradictory.
Before printing, water in the filament ruins the print. Nylon's stored schedule is 80 °C for 8 to 12 hours, and the accompanying note is unusually direct about how little time it takes to spoil a spool: one damp night on an open bench is enough. PETG asks for 65 °C over 4 to 6 hours and is far more forgiving of being ignored.
Worse, nylon reabsorbs during the print. A twelve-hour job on a spool that was dried this morning is printing wet filament by the afternoon, which is why serious nylon work runs from a heated dry box rather than from a dried spool. That is equipment PETG never asks for.
After printing, the part continues to take up water in service, and this is the part most people do not anticipate. An absorbed nylon part is dimensionally larger than the one that came off the plate, and its mechanical properties shift — tougher and more flexible, less stiff. For a gear meshing with another gear, or a bushing on a shaft, that is a fit changing over weeks.
PETG does none of this. It shrugs off water contact and its dimensions after a month in a damp shed are the dimensions it had on day one.
What nylon actually buys
Three properties PETG cannot offer, and they are the reason to accept everything above.
Abrasion resistance and self-lubrication. Nylon slides against metal and against itself with low friction and wears slowly. This is why printed gears, bushings, cable guides and wear strips are a nylon job and a poor PETG one.
Fatigue life. A nylon living hinge survives cycles that fracture PETG. Anything that flexes repeatedly rather than once belongs here.
Toughness at temperature. PA6's deflection range of 60 to 100 °C overlaps PETG's 68 to 80 but extends well past it, and nylon retains impact resistance where PETG becomes progressively less useful.
What it costs on the machine
Nylon carries a difficulty rating of 5 against PETG's 2, and the gap is made of specifics:
- An enclosure is required, not helpful. Unfilled PA6's shrinkage of 0.8 to 2.0% is the largest of any common filament and it warps off the plate without a warm chamber.
- The plate has to change. Nylon does not stick reliably to plain PEI; it wants garolite or a polyamide-specific sheet. PETG has the opposite failing: it welds itself to smooth PEI and takes the coating with it.
- Nozzle temperatures of 250–280 °C rule out hotends capped at 260.
- Price. $35–70 per kilogram for unfilled PA6, and $60–120 for the carbon-filled grade most people end up using, against $18–30 for PETG.
That last point is not the whole story on cost, and this is where the arithmetic is genuinely interesting.
A kilogram of nylon goes further than a kilogram of PETG
Nylon is the lighter polymer: PA6 at 1.14 g/cm³ against PETG at 1.27. For the same 1.75 mm filament, a kilogram of PA6 is 364.69 m and a kilogram of PETG is 327.36 m — 37.33 m more filament in the nylon spool, because PETG's 11.404% higher density costs it 10.236% of its length. Those extra thirty-seven metres matter most when the two spools are priced the same, which they often are. PA6's density is a band rather than a point, so the length and weight converter gives a truer figure once you have a specific spool in front of you.
The same effect runs through the part: an identical model printed in PA6 weighs meaningfully less than in PETG, so comparing the two by price per kilogram overstates nylon's premium by about a tenth. It is still a large premium. It is just not as large as the shelf price suggests, and on parts where mass matters — a drone arm, a moving carriage — the lighter part is a benefit in its own right.
Which to choose, by what the part does
- Slides, rubs, meshes or pivots against something — nylon, and specifically a filled grade if the part is at all large.
- Flexes repeatedly — nylon.
- Holds a dimension in a damp place — PETG, without hesitation.
- Lives outdoors — PETG. Nylon's outdoor rating is only fair, and its water uptake makes an outdoor nylon part a moving target.
- Just needs to be tougher than PLA — PETG. This covers most of what people come to nylon for.
- Contacts water continuously — PETG.
If you have decided on nylon, do not print PA6 unfilled
The most useful thing to know before buying is that the material almost everyone should actually use is carbon-filled. The fibre cuts shrinkage to between a quarter and three-tenths of unfilled PA6's, which converts a material that fights you off the plate into one that prints — PA6-CF against PA6 sets out what that costs in nozzle wear and money. Unfilled nylon has its place, mostly in small parts and living hinges, but it is not the default it appears to be.