Chopping short carbon fiber into a polyamide matrix moves tensile modulus from roughly 1,000-1,700 MPa for neat PA6/PA12 into the 6,000-8,100 MPa band, a 4-6× jump that is the single most-cited reason designers swap nylon for its filled cousin [S1][S2].
The reinforcement does not stop at modulus. The same Novamid ID 1030 CF10 dataset from Covestro shows yield stress rising from 72 MPa (unfilled) to 110 MPa, a 53% gain, while HDT at 0.45 MPa climbs from 84°C to 184°C, a 100°C shift that opens the door to under-hood and jigs-and-fixtures service [S2]. A separate generic FDM range puts CF-nylon tensile strength at 66-110 MPa and tensile modulus at 6,000-8,100 MPa, with flexural modulus of 4,300-6,500 MPa and HDT (0.45 MPa) at 150-190°C [S1].
Stiffness Headline Numbers, Side by Side
CF-nylon's tensile modulus sits in the 6,000-8,100 MPa window, with the X-X (along-fiber) direction hitting 7,625 MPa for Novamid ID 1030 CF10 against 2,720 MPa in the weaker X-Y (transverse) direction, an anisotropy ratio near 2.8× that prints into every part [S1][S2]. For comparison, neat PA6/PA66 typically reports tensile modulus in the 1,000-1,700 MPa range on FDM coupons, and that is before moisture conditioning which can drop neat nylon's effective stiffness further [S2][S5].
Flexural modulus tells the same story, 4,300-6,500 MPa for CF-nylon against roughly 1,000 MPa for unfilled nylon, which is why CF grades dominate drone frames, jigs, and structural brackets where bending deflection, not peak stress, drives the design [S1][S2]. The cost shows up in elongation: Novamid CF10 drops to 2.2-2.5% strain at break (X-X) versus 4.5% for the unfilled grade, a halving that is the first red flag for any impact-loaded use case [S2].
Heat, Creep, and Dimensional Stability
HDT at 0.45 MPa rises from 84°C (unfilled Novamid ID 1030) to 184°C for the CF10 version, a 100°C jump that is the most underappreciated gain in the dataset [S2]. Generic CF-nylon datasheets bracket HDT (0.45 MPa) at 150-190°C against roughly 120°C for plain nylon, putting filled grades into the same thermal neighborhood as many glass-filled nylons and well above what neat PA can survive in a warm enclosure [S1].
Creep resistance improves in parallel because the chopped fibers pin the polymer chains and slow viscous flow under sustained load, which is why CF-nylon is recommended for masking fixtures, conveyor components, and end-of-arm tooling where a neat nylon part would slowly sag [S2][S3]. Moisture absorption is not eliminated, both grades still take up water from humid air, but the filled version's stiffness advantage is large enough that wet-conditioned parts still usually outperform dry neat nylon in deflection-critical applications [S1][S5].
What You Lose: Toughness, Isotropy, and Surface
Standard nylon is selected when the part has to bend, dent, or absorb a drop without cracking; CF-nylon trades that toughness for rigidity and is "notably more brittle and prone to cracking under impact" despite the higher stiffness under static load [S1].
Anisotropy is the second tax. Tensile modulus of 7,625 MPa along the fibers versus 2,720 MPa transverse means a part printed in one orientation can be roughly 2.8× stiffer than the same STL rotated 90°, and the X-Y yield stress of 63 MPa is only 56% of the X-X 112 MPa [S2]. The chopped fibers also accelerate nozzle and extruder wear, so brass nozzles are usually retired in favor of hardened steel, and abrasive-slurry finishing on CF-nylon dust calls for proper PPE and dust extraction [S5].
Decision Matrix: When to Pick Which
Use plain nylon when impact, elongation, or wet-ductility dominates: snap-fit clips, living hinges, protective housings, and any part that must survive a drop. The roughly 4.5% strain at break and forgiving post-impact behavior are the design-enabling properties, not the 1,000-1,700 MPa modulus [S2].
Specify CF-nylon when the requirement is deflection, heat, or dimensional stability under sustained load: drone frames, manufacturing jigs, masking fixtures, air-management ducts, lever arms, and end-of-arm tooling [S1][S2][S3]. For comparison against other reinforced filaments, the CF-filled vs GF-filled nylon stiffness benchmark shows glass-filled nylon carrying the highest room-temperature modulus in one peer-reviewed study, but with a heavier density and different fiber-matrix interface behavior that trades off against carbon fiber's thermal conductivity and creep pinning [S4]. A side-by-side rule of thumb: if HDT or elastic-recovery under load is the failure mode, pick CF; if room-temperature modulus per gram is the only metric and you can tolerate the weight, glass-filled is a contender [S1][S2][S4].
Datasheet Caveats and Conditioning Discipline
No single "CF nylon modulus" exists. Drying, specimen conditioning, storage history, porosity, gripping, test speed, and test temperature can all change the reported number, so datasheet values should be read as method-specific rather than as one fixed truth for every filled spool [S5]. A number measured on an annealed, dry test bar is not an automatic design value for an as-printed, humid-conditioned part, and PA6-CF, PA11-CF, PA12-CF, and PA612-CF spools labeled "carbon fiber nylon" can print and test very differently even when their chopped-fiber content looks similar [S5].
Filament must be kept sealed and dried before use, partially used spools re-sealed, and a heated chamber is recommended to hit the published dimensional and mechanical numbers rather than a degraded coupon [S2]. Default printing parameters used by one service bureau are 0.25 mm layer height, 20% infill, 1 mm minimum wall, and 800 × 800 × 850 mm maximum build volume, with a part density of 1.52 g/cm³ and a stated accuracy of ±0.4% (lower limit ±0.4 mm) [S1].
Standards, Selection, and Trackable Signals
Industry-side material selection in this family is still driven by per-grade datasheets (Novamid ID 1030 CF10, PA6-CF, PA11-CF, PA12-CF, PAHT-CF, PPA-CF) rather than a single CF-nylon standard, because each chemistry pairs a different moisture response and thermal window with the chopped-fiber reinforcement [S2][S5]. ISO/ASTM 52900 terminology covers the material-extrusion process family used for these filaments, and ISO 527-style tensile bars plus ISO 75-style HDT bars are the usual mechanical test methods, but exact conformance should be confirmed against each vendor's declared test protocol [S5].
Trackable signals to watch: vendor moves toward higher-fiber-load (>15 wt%) PA6-CF and PA612-CF grades that close the X-Y/X-X modulus gap; published moisture-conditioned (rather than dry-as-molded) modulus curves; and published abrasive-wear-rate data on standard brass nozzles, since today's "use a hardened nozzle" advice is empirical rather than standardized [S2][S5]. For applications that sit between plastics and metals, the Eplus3D position that CF-reinforced nylon is "an ideal substitute for metal" for jigs, brackets, and tooling remains a useful framing, with the unspoken qualifier that it substitutes for aluminum in stiffness-critical, not impact-critical, roles [S3].