Carbon-Fibre-Reinforced Filaments: When to Choose PA6-CF, PC-CF, PPA-CF or PPS-CF
What does carbon fibre reinforcement add to a part — and what does it cost you? We compare the four carbon-fibre-reinforced materials we use with real datasheet values, and explain which one to choose for which application.
5 min readEksen 3 Boyut Engineering Team
In Short
- Carbon fibre reinforcement increases tensile strength, stiffness and heat resistance, and reduces moisture absorption in polyamides.
- In return, impact toughness usually drops: for parts that need to flex or absorb impacts, the unfilled material may be the better choice.
- In short: PA6-CF for general-purpose strong parts, PC-CF for stiffness and flame retardancy, PPA-CF for engine bays, PPS-CF for aggressive chemicals and high heat.
When people hear “carbon fibre”, most picture a very light, very strong material. Carbon-fibre-reinforced filaments used in 3D printing are different from woven carbon fibre sheets: they're made by adding short, chopped carbon fibres to an engineering plastic. In the materials we use, the fibre content is around 20% (15–20% for PPS-CF). The result is a part far stiffer and stronger than one made from the unfilled plastic — but it isn't the right choice for every application.
What Does Carbon Fibre Reinforcement Add?
- Higher tensile strength: in our datasheets, PA6's tensile strength rises from 70 ± 5 MPa to 102 ± 7 MPa in PA6-CF, and PC's from 65 ± 5 MPa to 95 ± 5 MPa in PC-CF.
- Higher stiffness: the fibres reduce how much the part flexes under load. For brackets, fixtures and load-bearing parts that must not flex, this is often the most important gain.
- Higher heat resistance: continuous service temperature rises from 100 °C to 120 °C for PA6, from 150 °C to 170 °C for PPA and from 200 °C to 220 °C for PPS.
- Better dimensional stability: polyamides absorb moisture. Carbon fibre reinforcement reduces this significantly — 24-hour water absorption drops from 2.80% in PA6 to 1.15% in PA6-CF.
- Matte surface: the matte finish of carbon-fibre filaments makes layer lines less visible than on unfilled materials.
What Do You Give Up?
Stiffness comes at a price: instead of flexing, the part carries the load directly and may not be able to absorb a sudden impact. That's why impact toughness drops for most materials. Polycarbonate is the most striking example: unfilled PC has a Charpy impact strength of 60 kJ/m², while PC-CF has 14 kJ/m². PA6 follows the same trend, from 18.0 kJ/m² to 12.5 kJ/m².
This rule doesn't apply to every material. Unfilled PPA and PPS are already stiff and relatively brittle; for them, carbon fibre reinforcement actually increases impact strength too (from 6.5 to 9.0 kJ/m² for PPA and from 5.0 to 7.5 kJ/m² for PPS).
Four Materials, Four Different Jobs
| Material | Tensile Strength | Continuous Service Temperature | Key Property | Typical Use |
|---|---|---|---|---|
| PA6-CF | 102 ± 7 MPa | 120 °C | High strength-to-weight ratio; resistant to oils, greases and solvents | Fixtures and jigs, structural components, rigid enclosures |
| PC-CF | 95 ± 5 MPa | 115 °C | Stiffness and heat resistance; UL94 V-0 equivalent flame retardancy | Brackets that need high stiffness, fixtures, robotic arms |
| PPA-CF | 140 ± 8 MPa | 170 °C | Highest strength; near-zero moisture absorption (0.10%); resistant to fuel, oil and antifreeze | Engine-bay brackets, exhaust-area components, high-load fixtures |
| PPS-CF | 120 ± 10 MPa | 220 °C | Very high chemical resistance; inherent UL94 V-0 flammability rating without additives | Aggressive chemical and high-temperature environments, semiconductor manufacturing fixtures |
Which One for Which Situation?
- A general-purpose strong part, working from room to moderate temperatures, at a reasonable cost: PA6-CF. It's often the first choice for production-line fixtures and jigs. Its moisture absorption is far lower than unfilled PA6 but not zero; if dimensional stability in a humid environment is critical, consider PPA-CF.
- A rigid part that must not flex, with somewhat higher heat and a need for flame retardancy: PC-CF. But if the part will take impacts (a protective enclosure, for example), toughness matters more than stiffness and unfilled PC may be the better choice.
- Engine bay, contact with hot oil, fuel or antifreeze, high mechanical load: PPA-CF. It has the highest tensile strength and the lowest moisture absorption of the four.
- Aggressive chemicals, continuous temperatures above 200 °C, or applications where non-flammability is mandatory: PPS-CF.
What to Watch Out for in Design
- Print orientation: carbon fibres largely align with the print direction, while strength between layers is lower than along them. Print orientation should therefore be chosen at the design stage according to the load the part will carry.
- Sharp corners and thin sections: stiff materials are more sensitive to stress concentrations. Rounding internal corners and avoiding very thin sections noticeably increases strength.
- Screw connections: for connections that will be assembled and disassembled often, metal threaded inserts should be used instead of tapping threads directly into the plastic.
- Tolerances: clearances for press-fit and snap-fit connections should take the material's stiffness into account — a material that doesn't flex can't tolerate a tight fit.
How to Read the Values in the Table
The values above are dry-state laboratory results from standard ISO test bars printed at 100% infill. A real part's performance depends on its geometry, print orientation and infill. These values are a strong starting point for comparing materials, but for a critical part the final decision should be made by evaluating the part's own conditions. You'll find the values for all our materials on our Materials page, and the official datasheets are available on request.
Tell us where your part will work, what load it will carry and what temperatures and chemicals it will face, and let's choose the right material together. Quotes are free of charge.