Nylon and PETG both show up in the same “engineering filament” conversations, and buying guides sometimes treat them as interchangeable upgrades from PLA. They are not close substitutes. PETG is close to a fire-and-forget material: print it, use it, store the spool loosely and it stays usable for months. Nylon rewards the exact same handling with a ruined print, because it pulls moisture out of the air fast enough to change how it prints within a day or two of being left open. The strength nylon offers only shows up if that moisture problem is managed.
Moisture is where these two materials actually diverge
PETG is close to hydrophobic: it does not pull in meaningful water from normal room air, which is a large part of why it tolerates loose spool storage better than most engineering filaments. Nylon is the opposite case, and how bad it is depends on which nylon. Data sheets for unreinforced PA6 put water absorption at saturation around 2.5 to 3.0 percent by weight at typical room conditions, and some sources cite figures as high as 9.5 percent under extended saturation testing. PA12, the nylon more commonly sold for 3D printing because it handles moisture better, absorbs far less: roughly 0.9 percent at full saturation and closer to 0.25 to 0.3 percent at 50 percent relative humidity, according to nylon material data sheets. Either way, both PA6 and PA12 outpace PETG’s moisture sensitivity by a wide margin, and community reporting on ruined prints after a spool sits open for 48 hours lines up with the data sheet numbers: nylon needs a dry box or an active drying routine that PETG simply does not.
Strength favors nylon, toughness leans toward PETG
On raw tensile strength, nylon comes out ahead. Comparisons of published data sheets put standard, unfilled PETG around 45 to 48 MPa, while unfilled PA6 and PA12 commonly range from about 60 to 80 MPa, with carbon-fiber-reinforced nylon blends pushing past 170 MPa in some manufacturer testing. That strength gap is a big part of why nylon shows up in gears, hinges, and load-bearing brackets where PETG would eventually fatigue. PETG answers back on toughness and impact resistance: it deforms and absorbs energy under a sudden impact rather than snapping, a property that makes it a more forgiving choice for parts that take an occasional knock rather than steady mechanical load. Nylon also brings real wear resistance and a low coefficient of friction to the comparison, which is why it turns up in printed gears and sliding parts that PETG is rarely used for.
Print setup: a wider gap than the two materials’ looks suggest
PETG prints in a fairly forgiving range, commonly 220 to 250°C at the nozzle with an optional heated bed around 50 to 75°C, and it does not require an enclosure on most desktop printers. Nylon runs hotter, typically 240 to 260°C with a bed around 60 to 80°C, and it benefits from an all-metal hotend and a warm, draft-free environment, since unenclosed nylon prints are more prone to warping than PETG. Between the elevated temperatures and the drying requirement, nylon is a bigger investment in equipment and routine before the first successful print, not just a different temperature setting on the same otherwise-similar process.
Cost and where each one actually wins
PETG remains the cheaper, more widely available option, with more brands competing at lower price points. Nylon sits in a narrower, pricier category, and the cost of a dry box or filament dryer to keep it usable adds to the real price of switching. Pick nylon for gears, hinges, brackets and other parts that face repeated mechanical stress or wear, provided you are willing to dry and store it properly. Pick PETG for functional parts that need to survive daily use and occasional impact without asking for a drying routine every time the spool comes out of storage.