PET-CF Carbon-fiber-reinforced PET (QIDI PET-CF / PET-CF17)

PET (polyethylene terephthalate) is the polyester of drink bottles and polyester fiber. Unlike PETG, which is modified to stay amorphous and easy to print, PET can partly crystallize, and that gives it much better heat resistance once the structure is set. PET-CF combines PET with chopped carbon fiber. QIDI sells it as PET-CF (listed as PET-CF17 in its comparison guide), and it's one of the most capable engineering composites we print.

For buyers, PET-CF's appeal is a rare combination: high stiffness, high heat deflection and low moisture uptake in one material. QIDI lists an HDT of 155.3 °C at 0.45 MPa, a tensile modulus of about 5600 MPa and water absorption of about 0.5 %. Carbon-fiber nylons can reach similar stiffness and heat, but they absorb far more water and change properties as they do; PET-CF stays much more consistent in humid environments.

The trade-offs are brittleness and layer strength. Elongation at break is only 2.2 % on QIDI's datasheet, and between-layer (Z) tensile strength on QIDI's comparison table is 25.2 MPa, much lower than its XY strength. PET-CF is a material for stiff, precise, warm-running parts, not for parts that must flex or take hard knocks.

QIDI also sells a glass-fiber sibling, PET-GF, and its data is a good example of why we read datasheets carefully. Its product page lists HDT 86.7 °C with no load stated, drying at 100–120 °C and says it doesn't need chamber insulation; QIDI's comparison guide lists HDT 120.3 °C at 0.45 MPa, a lower drying temperature and an enclosure as required. We treat the guide's values as the more consistent set, and quote PET-GF when you need a non-black color or a slightly tougher composite.

PET-CF is very stiff. QIDI lists an XY tensile modulus of 5629 MPa and XY tensile strength of 64.1 MPa on the product page, and a bending strength of 109.3 MPa on its comparison table. In practice, a PET-CF bracket deflects much less than the same bracket in PETG-CF or ASA-CF, which is what makes it valuable for alignment-critical parts.

Strength depends heavily on direction, because FDM parts are anisotropic: strongest along the printed layers (XY), weaker across them (Z). PET-CF's Z tensile strength on QIDI's table is 25.2 MPa, well under half its XY tensile strength. We orient your part so main loads run along the layers and will flag designs that force loads across them.

It is a brittle material in engineering terms. An elongation at break of 2.2 % means very little stretch before fracture. QIDI's Charpy impact figure of 25.3 kJ/m² is respectable for a composite, but sharp corners, thin sections and over-tightened screws are the usual causes of field cracks. Fillets, thicker sections and inserts address most of them.

QIDI also claims PET creeps less than nylon and polycarbonate under long-term load. That's a vendor claim without published creep data, but it's consistent with why PET-CF is chosen for sustained-load parts. For safety-relevant or permanently loaded parts, we recommend a test under real conditions.

QIDI lists PET-CF's heat deflection temperature (HDT, the point where a standard bar bends a set amount under load) at 155.3 °C at 0.45 MPa, and a Vicat softening temperature of 242.5 °C. QIDI doesn't say whether the HDT was measured on annealed or as-printed bars, and it publishes no higher-load (1.80 MPa) value, so we treat it as an upper-end, light-load figure rather than a working temperature.

Annealing (a controlled heat treatment after printing) helps PET crystallize and generally improves heat resistance and stiffness. QIDI's two pages disagree on the recipe: the comparison guide gives 120 °C for 10 h, while the product page gives 80–100 °C for 4–8 h. Annealing can cause slight shrinkage and dimensional change, and thin or large parts can warp, so we only anneal by agreement, after testing on your geometry.

As a guide, PET-CF is one of the most heat-tolerant materials we print, behind PPS-CF and the annealed high-temperature nylon composites. For any part that will run hot under load, tell us the temperature and load and we'll advise whether annealing or a different material is needed.

QIDI doesn't publish UV data for PET-CF. Polyesters are generally moderate in UV resistance; carbon black helps protect the surface, but over years of sun the matte finish can dull and fine features can lose toughness.

For long-term outdoor parts, ASA-CF is our default. Choose PET-CF outdoors when you need its heat resistance or stiffness and can accept some surface aging, or when a UV-protective coating is acceptable.

QIDI describes PET-CF as having excellent chemical resistance but gives no compatibility chart. PET generally resists oils, greases, fuels, many alcohols and dilute acids well, which suits automotive and machinery uses.

PET is generally vulnerable to strong alkalis, especially hot ones, and to some chlorinated and aromatic solvents. Acetone typically affects PET far less than ABS or ASA, but prolonged soaking isn't advised. If your part will see a specific fluid such as brake fluid, coolant or a cleaning chemical, tell us, and test a sample before committing to a batch.

Finished PET-CF parts absorb little water: about 0.5 % on QIDI's product page and 0.53 % saturated on its comparison guide. QIDI also states that moisture has no effect on PET-CF's mechanical properties and dimensional stability. That's a vendor claim, but it is the main reason to choose PET-CF over carbon-fiber nylon for parts in humid or wet environments.

The filament is a different story. PET-CF must be dried thoroughly before printing, and QIDI asks for storage below 15 % RH while printing. We dry it to QIDI's guidance and keep it sealed throughout; damp PET-CF prints with bubbles, rough surfaces and weak layers, which we won't ship.

PET-CF prints with a fine, uniform matte black finish that hides layer lines well. It looks like a molded engineering part, and most customers use it as printed.

With the 0.6 mm nozzle QIDI's wiki recommends, layer lines are slightly coarser and edges a little softer than with a 0.4 mm nozzle. We pick the nozzle per part: larger for reliability and strength on bigger parts, 0.4 mm where detail matters more.

Surfaces printed against the build plate are flattest. Support contact areas show as slightly rougher patches; tell us which faces are cosmetic so we keep supports off them.

Annealing is the main post-process for PET-CF. It can raise heat resistance and stiffness, but it also changes dimensions slightly and can warp thin or large parts. Because QIDI's own recipes differ, we test on a sample of your geometry first and only anneal by agreement.

Light sanding removes support marks but exposes fibers and leaves a lighter, fuzzy surface. Painting is possible with a suitable primer. Vapor smoothing isn't something we offer for PET-CF.

Heat-set inserts work well and are our standard for threads. Drilling and reaming are possible but wear tools faster than plain plastic. If parts are to be annealed, we usually install inserts afterward, as annealing can loosen them.

PET-CF is dimensionally stable. QIDI claims good dimensional stability with no warpage or shrinkage, attributing it to the fiber structure releasing stresses during printing. That's a vendor claim, but in practice PET-CF holds flatness and size well, especially compared with nylon composites, which can change size as they absorb water.

Holes print slightly undersized and outer dimensions slightly oversized, as with all FDM. For precise fits we compensate in the model or ream after printing. If parts will be annealed, expect a small additional dimensional change; we measure a sample before and after to plan for it.

Detail is limited by nozzle size. At 0.6 mm, very small text and thin ribs aren't practical; at 0.4 mm they're better but still not as crisp as PLA.