PETG-CF Carbon-fiber-reinforced PETG (PETG-CF)

PETG-CF is ordinary PETG with short, chopped carbon fibers mixed into it. PETG is the tough, slightly flexible plastic many water bottles are made from, modified with glycol so it prints cleanly. The fibers are not continuous strands like a carbon-fiber bicycle frame; they are tiny fragments that make the plastic stiffer and help it hold its shape as it cools.

For a buyer, the practical result is a part that feels more rigid and looks more 'engineered' than plain PETG, with a uniform matte, slightly frosted surface that hides layer lines well. QIDI's datasheet lists a tensile modulus (a measure of stiffness) of 3700 MPa and an XY tensile strength of 57 MPa, and describes the material as stronger and harder than ordinary PETG or PLA. It keeps most of PETG's chemistry, including its resistance to oils, greases and detergents.

What it does not do is turn PETG into a high-temperature plastic. QIDI's heat deflection temperature (HDT, the temperature at which a standard test bar bends by a set amount under load) is 77.0 °C at 0.45 MPa, only a few degrees above plain PETG Basic at 72.9 °C on the same table. Think of PETG-CF as 'stiffer, more stable PETG with a nicer finish', not as a substitute for ASA-CF, PET-CF or the nylons when heat is the problem.

QIDI also sells a glass-fiber sibling, PETG-GF. On QIDI's product pages it is slightly less stiff and strong (51 MPa tensile, HDT 76 °C, load not stated) and a little lighter (1.26 g/cm³ against 1.31 g/cm³ for PETG-CF). Glass fiber usually costs less and comes in more colors because it isn't inherently black; we can quote either if color matters more than the last bit of stiffness.

The headline benefit is stiffness. Carbon fibers resist stretching far better than the surrounding plastic, so a PETG-CF bracket deflects less under the same load than a plain PETG one. QIDI lists a bending strength of 89.5 MPa in the XY direction in its filament comparison guide, and an XY tensile strength of 57 MPa on the product page.

Every FDM part is anisotropic, meaning its strength depends on direction. Along the printed lines (XY) the material is at its best; between layers (Z) it relies on how well each new layer fuses to the one below. QIDI's guide gives PETG-CF a Z tensile strength of 28.0 MPa, compared with 37.52 MPa for plain PETG Basic. In other words the fibers make the part stiffer within a layer but slightly weaker across layers, which is common for fiber-filled filaments.

That trade-off is why orientation matters so much. We orient your part so the main bending or pulling loads run along the layers wherever we can, and we will tell you if a design forces a weak orientation. For brackets, hooks and clips, a small change such as printing on its side instead of standing up can make a bigger difference than switching materials.

PETG-CF is less forgiving than plain PETG when overloaded. Plain PETG tends to bend and whiten before it breaks; PETG-CF holds its shape longer and then fails more suddenly. If your part's job is to survive drops and abuse rather than to stay rigid, plain PETG, TPU or a nylon composite is usually the better call.

QIDI publishes an HDT of 77.0 °C at 0.45 MPa (the lighter of the two standard test loads) and a Vicat softening point of 83 °C, the temperature at which a loaded needle sinks into the surface. Those are short-term lab figures for a test bar, not a safe working temperature for a loaded part. Under steady load, PETG-CF will start to creep (slowly deform) well below them.

As a rule of thumb, treat PETG-CF as comfortable in normal indoor conditions and warm machinery spaces, but not as a heat-resistant material; its heat rating in this guide is low for that reason. If your part sits near a motor, a heater, a hot light or anything you can't comfortably keep your hand on, tell us. We would usually suggest ASA-CF, PET-CF or a high-temperature nylon composite instead.

QIDI documents optional annealing for PETG-CF at 80–90 °C for 2–4 h. That range is above the material's HDT, so parts can sag, shrink or warp during the process. We don't anneal PETG-CF by default and rarely recommend it.

QIDI doesn't publish UV-resistance data for PETG-CF. PETG generally holds up better outdoors than PLA but is not a dedicated UV-stable plastic like ASA. The black, carbon-filled color hides early fading better than bright colors do, but long-term sun can still dull the matte surface and make thin features more brittle.

For signage, garden hardware, marine fittings or anything mounted in full sun for years, we'd recommend ASA-CF or plain ASA instead. For shaded or covered outdoor use, PETG-CF is usually a sensible, economical option.

QIDI states that PETG-CF inherits PETG's resistance to most oils, greases and detergents. That makes it a reasonable choice for guards and covers around lubricated machinery, and for parts that get wiped down with soapy cleaners.

PETG is generally less resistant to strong solvents. Acetone, some paint thinners and aggressive degreasers can soften, craze or swell the surface, and repeated contact with fuels is not something we would rely on. Isopropyl alcohol wipes are generally tolerated for cleaning, but prolonged soaking is not advised. If your part will see a specific chemical, tell us, and test a sample part in the real fluid before committing to a production run.

As filament, PETG-CF picks up moisture from the air, and QIDI describes it as highly hygroscopic (moisture-absorbing). Damp filament prints with bubbles, stringing, rough surfaces and weaker layers. We dry it before printing to QIDI's guidance and keep it in a dry box or the heated QIDI Box during long jobs, so this is our problem rather than yours.

Finished PETG-CF parts are a different story. Once printed, PETG-based parts absorb far less water than nylon parts and keep their stiffness and dimensions in humid rooms, so you don't need to store them specially. That stability is one reason PETG-CF is a good everyday alternative to carbon-fiber nylon when heat isn't a concern.

PETG-CF's main visual appeal is a uniform matte, slightly frosted black surface with a subtle grain. It hides layer lines much better than glossy plain PETG, so parts look like finished products rather than prototypes. Small surface flaws and stringing are also less visible.

The flip side is that the surface is slightly rough and can feel a little dusty when new; the texture comes from fibers near the surface. Color choice is limited because carbon fiber is inherently black or very dark grey. If you need a specific color or a lighter shade, ask about PETG-GF, which uses glass fiber and is available in more colors.

Surfaces printed against the build plate come out flatter and more even than top surfaces, which can show slight texture. Tell us which faces are cosmetic and we'll orient the part to favor them, within the limits of strength and supports.

PETG-CF can be lightly sanded, but sanding exposes fibers and can leave a fuzzy, lighter-colored surface, so it is best kept to removing support marks or blending small areas. Wear a dust mask if you sand fiber-filled parts yourself, and avoid breathing the dust.

Vapor smoothing is not something we offer for PETG-CF; it doesn't work on this material the way it does on ABS. Painting is possible with the right primer, but most customers choose PETG-CF precisely because its natural finish doesn't need paint.

Heat-set brass inserts install well in PETG-CF and are our usual recommendation for threads that will be assembled more than a few times. Holes can be drilled or reamed to size; use sharp bits because the fibers dull tools faster than plain plastic. Annealing is possible but, as noted above, risks distortion, so we only do it by agreement on a specific part.

PETG-CF is one of the more dimensionally stable materials we print. QIDI notes that the chopped fiber gives greater dimensional stability and low shrinkage, and in practice flat parts warp less than in plain PETG, ABS or nylon. That makes it a good choice for fixtures, panels and parts that must sit flat.

Like every FDM material, small holes tend to print slightly undersized and outer dimensions slightly oversized, by a fraction of a millimeter depending on geometry. For press-fits, bearings or shafts, we either compensate in the model or print slightly undersized and ream to size. If a dimension is critical, mark it on your drawing so we can check it, and consider ordering one test part before a batch.

Fine features are limited by the nozzle. Because fiber-filled filaments can't go through a 0.2 mm nozzle, very small text, sharp internal corners and thin ribs are softer than they would be in PLA. QIDI's wiki also notes that larger nozzles reduce clog risk at the cost of precision, so we choose the nozzle per part to balance detail and reliability.