Key takeaways
- Stiff, tough and heat-resistant are three separate axes. No material in this group leads on all three.
- PC is notch-sensitive: PolyLite PC's **notched** impact is only 4.1 kJ/m², lower than PLA. The modified PC grades are the tough ones — 21.3 to 25.8 kJ/m².
- PA6-GF is the only one that holds its shape above 150 °C, and also the one that wears nozzles hardest.
- The whole group needs an enclosure and drying. The equipment usually costs more than the difference in material price.
When PETG and ABS aren't enough, people tend to jump straight to the biggest number on the data sheet and buy that. It is the quickest way to pay for a property your part doesn't need while missing the one it does.
Engineering materials have three axes, and they are nearly independent: stiffness (how much the part deforms under load), toughness (how much energy it absorbs before breaking), and heat ceiling. Choose the axis first, then the material.
Five candidates, side by side
| CoPA | PA6-CF20 | PA6-GF25 | PolyLite PC | PC-ABS | |
|---|---|---|---|---|---|
| Tensile strength | 78.0 MPa | 109.3 MPa | 80.1 MPa | 69.1 MPa | 39.9 MPa |
| Notched impact | 6.9 kJ/m² | 11.0 kJ/m² | 10.0 kJ/m² | 4.1 kJ/m² | 25.8 kJ/m² |
| HDT 0.45 MPa | 111 °C | 215 °C | 191 °C | 111 °C | 112 °C |
| Vicat softening | 180 °C | 219 °C | 212 °C | 120 °C | 135 °C |
| Enclosure | 45 °C | 50 °C | 55 °C | 50–60 °C | 45–55 °C |
| Nozzle | Standard | Hardened 0.4 | Hardened 0.6 | Standard, 300 °C | Standard |
Read the impact and heat rows together. The glass-filled nylon holds its shape far hotter than any PC, while the modified PC absorbs more than twice the notched impact energy. They are close to opposite materials, and nothing in the table tells you which is "better".
Stiff means it doesn't bend. Tough means it doesn't break. Very few materials give you both.
PA12 — tough, and that is the whole point
Unreinforced nylon is the most ductile material in this group: it bends a long way before it breaks. One thing the usual comparison tables gloss over: none of the manufacturers we could check publish elongation for FDM nylon, so any "180 % elongation" figure you read somewhere deserves suspicion. It isn't stiff either — design for stiffness and it will disappoint you. But for living hinges, snap fits and parts that take repeated knocks, nothing in the catalogue replaces it.
Watch the 1.2 % shrinkage, the highest in the group. Parts that must fit closely need a tolerance test print before running a batch.
PA-CF — mechanical parts for real use
This is the closest an FDM printer gets to a CNC-machined part: Polymaker publishes a modulus above 8,600 MPa and an HDT of 215 °C for Fiberon PA6-CF20 (annealed), with a self-lubricating surface where things slide. Gears, bushings and production fixtures are its home ground.
The cost isn't in the spool but in the process. PA-CF absorbs moisture so readily that one afternoon in the open is enough to ruin a print, so it needs a heated dry box running throughout the print, not just drying beforehand. More in the PA-CF article and how to dry filament.
PA6-GF — when heat is the real constraint
An HDT of 191 °C takes PA6-GF out of comparison with the rest. If the part works in an engine bay, next to another machine's nozzle, or in an industrial drying oven, it is the only FDM choice in the group.
The price is three things: glass fibre wears nozzles harder than carbon fibre, so it needs a 0.6 mm hardened nozzle; PA6 absorbs moisture even more readily than PA12; and the chamber must hold 55 °C, more than most home enclosures can manage.
PC Core and PC Blend — when impact comes first
This is where PC is most misunderstood. Bulk polycarbonate is famously impact-resistant, but a notched printed part isn't: Polymaker publishes 4.1 kJ/m² for PolyLite PC, lower than PLA. PC is notch-sensitive — intact it is extremely tough, but with a cut already in it, a crack runs straight through. What it certainly has is stiffness (tensile modulus 2,497 MPa, bending strength 106.1 MPa — the highest among the amorphous plastics) and an HDT of 111 °C. For machine guards, lamp housings and load-bearing frames at risk of knocks, it is the clear answer.
Modified PC is the easy-printing version: nozzle temperature and difficulty drop to ABS levels. And here is the surprise in the data — it gives up almost nothing: Polymaker publishes an HDT of 112 °C for PC-ABS (PolyLite PC is 111 °C) and 25.8 kJ/m² notched impact, six times tougher than plain PC. What it loses is tensile strength, 39.9 vs 69.1 MPa. For most workshops stepping up from ABS, it is a more sensible step than jumping straight to PC Core.
Choose by the job
Four common cases
- Gears, bushings, production fixtures
- PA-CF — stiff, dimensionally stable, self-lubricating
- Living hinges, snap fits, parts that take repeated knocks
- Unreinforced nylon — the most ductile in the group; test it yourself, since elongation isn't published
- Engine-bay parts, fixtures that run hot
- PA6-GF — HDT 191 °C
- Machine guards, lamp housings, frames at risk of impact
- Modified PC — 25.8 kJ/m² notched at HDT 112 °C, not plain PC
The real cost of this group
The 2× to 3× price index over PLA is the visible part. Three other items are usually larger:
- Equipment. An enclosure holding 50–55 °C, a heated dry box running during the print, a 300 °C hot end, a hardened nozzle. A one-off cost but not a small one, and missing any piece means the material won't reach its data-sheet figures.
- Failure rate. This group fails noticeably more than PLA and PETG, especially on large parts. Use your workshop's real rate in the cost rather than a general factor.
- Machine hours. Print speeds of 30–80 mm/s against 60–150 for PLA. A part can take twice as long.
That doesn't make the group expensive — it means comparing on price per kilogram leads to the wrong decision. When a PA-CF part replaces a machined aluminium part, the material price index stops being a meaningful variable. The full method is in the cost article, and the options for a printer that isn't ready yet are in the substitution guide.
Frequently asked
Is nylon or polycarbonate stronger?
It depends what you mean by strong. PA6-GF25 has 80.1 MPa tensile strength and an HDT of 191 °C, so it resists deformation and heat far better. PolyLite PC, on the other hand, reaches only 4.1 kJ/m² notched impact against PA6-GF25's 10.0 — the opposite of most people's intuition. If you need both tough and stiff, a modified PC is a much better answer. For statically loaded parts choose reinforced nylon; for parts at risk of impact choose PC.
Which FDM material in this catalogue resists heat best?
Reinforced nylon: PA6-CF20 reaches an HDT of 215 °C and PA6-GF25 191 °C on annealed specimens, ahead of PC at 111 °C. All three need an enclosure, and the two fibre-filled grades need a hardened nozzle. In resin, High Temp Resin reaches 238 °C, but only after a thermal post-cure at 160 °C; UV cure alone gives 142 °C.
Can PA-CF or PC be printed on an open-frame printer?
Not for any part of meaningful size. PA-CF needs a 50 °C chamber and PC 50–60 °C; without chamber heat the part warps at the corners or delaminates. PA6-GF is stricter still at 55 °C. If your printer has no enclosure, PETG-CF is the closest option, at a much lower level of performance.
How is PC Blend different from PC Core?
Modified PC is blended to be easier to print: a 250–275 °C nozzle instead of 265–300 °C, and a 45–55 °C chamber instead of 50–60 °C. On Polymaker's published figures it gives up almost no heat resistance (112 vs 111 °C) and is much tougher notched (25.8 vs 4.1 kJ/m²); the cost is tensile strength, 39.9 vs 69.1 MPa. For most workshops stepping up from ABS, that is a sensible trade.
Why is PA12 an engineering material if its modulus is low?
Because stiffness isn't the only property with engineering value. Unreinforced nylon bends a long way before breaking, so it survives millions of flex cycles and knocks that shatter every stiffer material. Living hinges and snap fits need exactly that.