This is a comparison between two answers to different questions that get asked in the same words. Someone says "I need the strongest material my printer can handle" and is pointed at either polycarbonate or a nylon, largely at random. They are not interchangeable, and the part usually knows which one it wants.
Polycarbonate is stiff, dimensionally stable in service, transparent-ish, and brittle in the specific sense that it does not tolerate being scraped or abraded. Nylon is tough, slippery, fatigue-resistant, and will not hold a dimension in a damp room. Almost everything else follows from that pair of sentences.
What the selector says when you ask for both
Weight strength and heat resistance at the top of the scale, leave ease of printing at the bottom, and give the selector a capable enclosed machine — a 300 °C hotend and a hardened nozzle. Four materials come back, ranked:
- PPA (high-temp nylon) — the top scorer, and immediately disqualified for most readers by its own weakness list: it wants a heated chamber no consumer machine has, and it is the dearest material here.
- PA6-CF, score 0.7968, with strength and heat contributing almost equally to it.
- PA6-GF, score 0.7516.
- Polycarbonate, score 0.7063, and the only one of the four whose stored weakness list names ultraviolet.
Two machines are ruled out of the running entirely: ULTEM and PEEK both need more nozzle temperature than this machine has. Raise the maximum nozzle temperature and those two disqualifications disappear, which is the useful thing about doing this in the material selector rather than from a table: the ranking is a function of the machine you own, not a property of the plastics.
The interesting result is that filled nylon outranks polycarbonate on a pure strength-and-heat brief, which is not what most people expect. PA6-CF's deflection range of 120–190 °C beats PC's 110–140, and its 80–130 MPa tensile beats PC's 60–70.
But a ranking is not a recommendation, and the selector's own caveats are where the decision actually lives.
Where polycarbonate is the right answer
The part must hold its dimensions in service. This is the big one. PC absorbs very little water; nylon absorbs a great deal. A PC housing measured in January is the same housing in July, and a nylon one is not.
You need to see through it. Nothing in the nylon family competes. PC is the only structural filament here that produces a usefully translucent part.
The load is steady and the part must not deflect. PC is stiffer than unfilled nylon by a wide margin and does not creep under sustained load the way a moisture-laden nylon will.
You want a material that behaves like a plastic when you machine it. PC drills, taps and cuts predictably. Nylon is gummy and grabs a drill bit.
Where nylon is the right answer
Anything that rubs. Nylon is self-lubricating and wear-resistant; PC is neither. Gears, bushings, cable guides, wear strips and sliding surfaces are a nylon job, and putting PC there produces a squeaking part that polishes itself away.
Anything that flexes repeatedly. Nylon's fatigue life in bending is far better. Living hinges, spring clips and anything cycled belong here.
Impact at the edges. PC is impact-resistant in the bulk but unforgiving where a corner is knocked; nylon deforms and recovers.
Above 140 °C. PC's ceiling ends; PA6-CF and PPA keep going.
What they share, and it is a lot
Both sit at difficulty 5. Both need an enclosure — actively heated, for either, if the part is large. Both must be dried hard before printing, PC at 90 °C for 6 to 12 hours and PA6 at 80 °C for 8 to 12, and both suffer irreversible chain scission if printed wet rather than merely printing badly.
Both also want a specialist build surface: PC-specific sheets with adhesive for polycarbonate, garolite for nylon. Neither sticks reliably to plain PEI.
So the printer requirements do not separate them. If you can run one, you can very likely run the other.
The blends and fills that change the answer
Neither material is usually printed in its pure form on a desktop, and the modified grades shift the comparison substantially.
PC-ABS trades some heat resistance for much easier printing and lower shrinkage — the sensible choice if your requirement was "hotter than ABS" rather than "genuinely above 110 °C". PC against ABS works through where that line falls.
PA6-CF is what most people mean by printed nylon, because unfilled PA6's shrinkage makes large parts impractical. It also stiffens the material toward PC's territory while keeping some of nylon's wear behaviour, which narrows this whole comparison — PA6-CF against PA6 covers what it costs.
PA12 absorbs far less water than PA6, which removes nylon's biggest disadvantage against PC at the price of stiffness.
Ultraviolet, where neither is good and one is worse
Both carry the same outdoor rating of fair, and the selector gives them the same contribution for it — but they get there differently and the failure looks different.
Polycarbonate yellows. Its stored weakness list names ultraviolet exposure without a coating explicitly, and a clear PC part that has spent a summer outdoors is visibly amber and has lost some of its impact resistance with the colour.
Nylon's outdoor problem is compounded by moisture: ultraviolet degradation happens alongside dimensional movement from water uptake, so an outdoor nylon part changes size as well as condition. PA12 is the exception here, rated good outdoors, and it is the polyamide to pick if the part has to live outside.
If the part is genuinely outdoors and structural, though, the better answer is usually neither of these — ASA or a filled PETG will do the job with a fraction of the difficulty.
Deciding in one question
Ask what the part does when it fails.
If it fails by wearing out, fatiguing or being flexed to death, it is a nylon part, and the moisture problem is something you design around with clearance and a filled grade.
If it fails by drifting out of tolerance, deflecting under load or needing to be seen through, it is a polycarbonate part, and the corner lift is something you design around with chamfers and a hot chamber.