PET-CF vs PA-CF vs PC: Tensile Strength for Functional Parts
Why Carbon Fiber Reinforcement Changes the Equation
Carbon fiber chopped-strand reinforcement does two things to a base polymer: it dramatically increases stiffness (flexural modulus) and usually raises tensile strength, but it reduces elongation at break and impact toughness. The trade-off is a stiffer, stronger part that can shatter rather than deform — ideal for rigid structural brackets and housings, but a poor choice for parts that must absorb shock.
The three materials in this comparison cover different territory on that trade-off. PA-CF maximizes raw tensile strength. PET-CF (specifically true PET base, not PETG) brings meaningful heat resistance to a CF composite without requiring an enclosed chamber. PC offers the best impact resistance of the three — with or without carbon fiber — at the cost of demanding print conditions.
Tensile Strength: The Raw Numbers
Tensile strength (MPa) measures pull-force resistance before fracture. For functional parts under sustained axial load — brackets, fastener surrounds, lever arms — it is the primary property to optimise.
PA-CF: The Clear Winner on Tensile Strength
Carbon-fiber nylon consistently posts the highest tensile strength of any desktop-printable CF composite. Across our database:
- Bambu Lab PA6-CF: 102 MPa tensile, 5,460 MPa flexural modulus, HDT 164°C
- Fiberon PA6-CF20: 109.3 MPa tensile, 7,037.6 MPa flexural modulus, HDT 215°C
- eSUN PAHT-CF: 173.4 MPa tensile, 5,612 MPa flexural modulus, HDT 190°C
- 3DXTech CarbonX HTN+CF: 87 MPa tensile, 7,895 MPa flexural modulus, HDT 240°C
- Elegoo PAHT CF: 87 MPa tensile, 5,089 MPa flexural modulus, HDT 193°C
- Bambu Lab PAHT-CF: 92 MPa tensile, 4,230 MPa flexural modulus, HDT 170°C
The spread is wide — Eryone PA6-CF measures only 53 MPa while eSUN PAHT-CF reaches 173 MPa — which reflects differences in CF loading percentage, PA grade (PA6 vs PA12 vs PAHT/PA66), and testing methodology. As a working benchmark, expect 80–110 MPa from a mid-range PA6-CF product.
PET-CF vs PETG-CF: An Important Distinction
The "PET-CF" label covers two distinct material families that perform very differently. True PET-CF (polyethylene terephthalate base) operates at significantly higher temperatures than PETG-CF (glycol-modified PET). Most filaments marketed as "PET-CF" in the budget segment use PETG as their base.
Representative PETG-CF tensile data from our database:
- Bambu Lab PETG-CF: 35 MPa tensile, 2,910 MPa flexural modulus, HDT 68°C
- BASF Ultrafuse PET CF15: 63.2 MPa tensile, 5,452 MPa flexural modulus, HDT 72°C
- 3DJAKE easyPETG CF: 72 MPa tensile, 2,860 MPa flexural modulus, HDT 68°C
- Prusament PETG-CF: 47 MPa tensile, HDT 96°C
- Fiberlogy PETG+CF: 105 MPa tensile, HDT 69°C
True PET-CF (unmodified PET base) posts meaningfully higher heat deflection temperatures:
- Bambu Lab PET-CF: 74 MPa tensile, 5,320 MPa flexural modulus, HDT 182°C
- Fiberon PET-CF17: 65.9 MPa tensile, 4,744 MPa flexural modulus, HDT 147.5°C
- Spectrum PET CF15: 80 MPa tensile, HDT data unavailable
The HDT gap between true PET-CF (147–182°C) and PETG-CF (68–96°C) is enormous. If your functional part sees temperatures above 70°C — engine bay proximity, outdoor summer exposure, dishwasher proximity — PETG-CF will deform while true PET-CF stays rigid.
PC: Strong but Outgunned on Tensile
Unfilled polycarbonate is a high-performance engineering polymer, but its tensile strength on its own sits in a range that PA-CF exceeds comfortably:
- Polymaker PolyCore PC-7413: 74.6 MPa tensile, HDT 139°C
- Overture PC Professional: 70.2 MPa tensile, 2,588 MPa flexural modulus
- Prusament PC Space Grade: 72 MPa tensile, HDT 137°C
- Bambu Lab PC: 55 MPa tensile, HDT 117°C, impact strength 34.8 kJ/m²
- 3DXTech 3DXMAX PC: 62 MPa tensile, HDT 135°C
Adding carbon fiber to PC raises stiffness substantially:
- 3DXTech CarbonX PC+CF: 70 MPa tensile, 5,890 MPa flexural modulus, HDT 135°C
- 3DXTech CarbonX ezPC+CF: 73 MPa tensile, 6,540 MPa flexural modulus, HDT 119°C
- IEMAI CF-PC: 72 MPa tensile, 5,880 MPa flexural modulus
PC+CF narrows the tensile gap with PA-CF but does not close it. Where PC+CF does compete effectively is on the flexural modulus — 5,890–6,540 MPa for PC+CF is comparable to PA6-CF (4,230–7,038 MPa), meaning the two produce similarly stiff parts at similar CF loadings.
Head-to-Head Property Comparison
| Property | PETG-CF (typical) | PET-CF (true PET base) | PA6-CF (typical) | PC unfilled (typical) | PC+CF (typical) |
|---|---|---|---|---|---|
| Tensile strength | 35–72 MPa | 65–80 MPa | 87–110 MPa | 55–75 MPa | 70–73 MPa |
| Flexural modulus | 2,900–5,740 MPa | 4,744–5,320 MPa | 4,230–7,038 MPa | 1,890–2,900 MPa | 5,420–6,540 MPa |
| Heat deflection (HDT) | 68–96°C | 147–182°C | 147–215°C | 108–141°C | 119–135°C |
| Elongation at break | 2–10% | 2–5% | 2–14% | 4–14% | 2% |
| Impact toughness | Low–moderate | Low | Moderate | High | Low |
| Moisture sensitivity | Low | Low | High — must dry | Moderate | Moderate |
| Enclosure required | No | No | Recommended | Yes | Yes |
| Abrasive nozzle wear | High | High | High | Low | High |
| Print temp range | 220–270°C | 260–300°C | 255–300°C | 250–295°C | 275–300°C |
Heat Deflection Temperature: Where the Comparison Reverses
If tensile strength were the only property that mattered, PA-CF would win every comparison. But functional parts often operate at elevated temperature, and that changes the ranking significantly.
PETG-CF's Achilles heel is thermal performance. Most PETG-CF products have HDT values of 68–74°C (Bambu Lab PETG-CF: 68°C; Eryone PETG-CF: 68°C; Elegoo PETG CF: 73.9°C). A part left inside a car on a summer day — where cabin temperatures routinely reach 70–80°C — can deform under its own weight. For outdoor functional applications, this rules out PETG-CF entirely.
True PET-CF dramatically improves on this. Bambu Lab's PET-CF reaches 182°C HDT, and Fiberon PET-CF17 reaches 147.5°C — making them viable for underhood proximity, enclosed electronics, and industrial mounting that would immediately disqualify PETG-CF.
PA6-CF matches or exceeds true PET-CF on thermal resistance. Fiberon PA6-CF20 reaches 215°C HDT; 3DXTech's CarbonX HTN+CF reaches 240°C. For high-temperature functional parts, high-temperature PA-CF products are the engineering choice when you need both strength and heat resistance.
Standard unfilled PC falls in the middle. Most PC filaments in our database show HDT between 108°C (Bambu Lab PC FR: 108°C) and 141°C (3DXTech TriStat ESD-PC: 141°C). This is a genuine advantage over PETG-CF but falls short of the best PA-CF and true PET-CF grades.
Impact Resistance and Part Durability
Carbon fiber reinforcement trades toughness for stiffness. All three CF variants in this comparison are more brittle than their unfilled equivalents. This matters significantly for parts that experience sudden loads — hammer strikes, drops, fastener overtorque.
Among the CF variants, PA-CF retains more toughness than PC-CF or PET-CF due to nylon's inherent energy absorption. Bambu Lab PA6-CF measures 40.3 kJ/m² Charpy impact strength; Bambu Lab PAHT-CF reaches 57.5 kJ/m². These are notably higher than BASF Ultrafuse PET CF15 at 5.7 kJ/m² or 3DJAKE easyPETG CF at 4 kJ/m².
Unfilled PC is the impact resistance champion. Bambu Lab PC measures 34.8 kJ/m²; Elegoo PC reaches 76.5 kJ/m². For enclosure panels, covers, and anything subject to shock loading, unfilled PC significantly outperforms all CF variants. Adding CF to PC (as in 3DXTech CarbonX PC+CF at ~2% elongation) largely destroys PC's toughness advantage — you get stiffness comparable to PA-CF but lose the impact behaviour that makes PC valuable.
Printability and Setup Requirements
All three material classes require a hardened-steel nozzle due to the abrasive carbon fibre content. Beyond that, their printing requirements diverge significantly.
PETG-CF is the most accessible. Print temperatures of 230–270°C and bed temperatures of 60–90°C are achievable on most open-frame printers. No enclosure is needed. It requires no special drying before a first print (though drying after opening is recommended). This makes it the practical choice for users who want CF aesthetics and improved stiffness without adding complexity.
True PET-CF demands higher temperatures — Bambu Lab PET-CF specifies 260–290°C nozzle and 80–100°C bed — and benefits from an enclosure to prevent warping. Fiberon PET-CF17 requires 270–300°C. The extra heat resistance comes with a cost in print difficulty.
PA-CF is humidity-sensitive above all. Nylon absorbs moisture rapidly, and wet PA-CF produces stringing, bubbling, and weak layer bonds. Drying at 80°C for 8–12 hours before printing is non-optional for good results. Print temperatures typically run 255–300°C with bed temperatures of 80–110°C. An enclosure is recommended for PA6-CF and required for high-temperature PA variants. The reward is the highest achievable tensile strength and heat resistance among open-material desktop printing options.
PC is the most demanding of all. Successful unfilled PC printing requires a fully enclosed, heated chamber (typically 50–70°C ambient), bed temperatures of 90–120°C, and careful first-layer adhesion management. PC warps aggressively on open frames. Adding CF to PC compounds the shrinkage behaviour. For most desktop users, unfilled PC is the upper limit of practically printable materials; PC+CF pushes into territory that requires commercial enclosures or purpose-built high-temp printers.
Which Material Wins for Specific Functional Parts?
Brackets and structural clips under sustained tension
Winner: PA-CF. The tensile strength advantage (87–110 MPa vs 55–74 MPa for PC or 35–80 MPa for PET/PETG-CF) directly translates to smaller cross-sections holding the same load. Bambu Lab PA6-CF (102 MPa, 5,460 MPa flexural modulus) and Fiberon PA6-CF20 (109.3 MPa, 215°C HDT) are representative choices.
Enclosures and housings subject to impact
Winner: unfilled PC. Bambu Lab PC (34.8 kJ/m² impact, 55 MPa tensile, 117°C HDT) and Elegoo PC (76.5 kJ/m² impact, 54 MPa tensile) absorb shock far better than any CF variant. Use PC when the part must flex slightly on impact rather than fracture.
Under-bonnet or high-temperature functional parts
Winner: PA-CF or true PET-CF, depending on setup. For temperatures above 150°C, high-temp PA-CF (3DXTech CarbonX HTN+CF: 240°C HDT; Fiberon PA6-CF20: 215°C HDT) is the only open-material desktop option. For the 80–180°C range where printing difficulty must be minimised, Bambu Lab PET-CF (182°C HDT, 74 MPa, no enclosure required) is a strong choice.
Rigid prototypes and tooling jigs with tight tolerances
Winner: PA-CF or PC+CF. Both deliver flexural modulus above 5,000 MPa — comparable to glass-filled nylon — which minimises deflection under load. The choice between them depends on whether you need higher tensile strength (PA-CF) or better impact tolerance (PC+CF over PA-CF, though still brittle).
Entry-level CF printing without an enclosure
Winner: PETG-CF. If you're printing on an open-frame machine and want CF stiffness and appearance, PETG-CF is the accessible option. Just accept HDT below 80°C. BASF Ultrafuse PET CF15 (63.2 MPa, 5,452 MPa flexural modulus, 72°C HDT) offers the best combination of stiffness and print accessibility in this segment.
Summary: Matching the Material to the Load Case
There is no single winner in this comparison — each material occupies a distinct performance niche.
- PA-CF wins on tensile strength (87–170 MPa) and heat resistance (147–240°C HDT). The cost is mandatory drying, enclosure preference, and moisture sensitivity in service.
- PET-CF (true PET base) fills the gap between PETG-CF and PA-CF: better heat resistance (147–182°C HDT) than PETG-CF with simpler printing than PA-CF, but modest tensile strength (65–80 MPa).
- PETG-CF is the accessible entry point: stiffness improvement over unfilled PETG, no enclosure required, HDT limited to 68–96°C, tensile strength 35–72 MPa. Suitable for low-temperature rigid parts only.
- PC (unfilled) is the toughness choice: 34–76 kJ/m² impact strength that CF variants cannot approach. Use it where parts must absorb sudden shock rather than sustain static tensile load.
- PC+CF maximises PC stiffness (5,420–6,540 MPa flexural modulus) at the cost of PC's toughness advantage. Only worthwhile if you specifically need PC-level HDT (119–135°C) combined with high flexural rigidity and are willing to print in a fully heated enclosure.