PET-CF vs PETG-CF: checking the material before buying

Stated polymer and thermal entries in the two sheets

The PET-CF17 TDS describes carbon-reinforced PET and lists melting at 241.3°C and crystallization at 202.9°C by DSC at 10°C/min. The PETG-rCF08 TDS describes PETG reinforced with recycled carbon fiber and lists N/A for both measurements. That difference identifies the published entries; N/A is neither zero degrees nor a polymer-structure analysis by itself. Keep the name and method with each datum when preparing a comparison. The available entries must not be converted into an unstated material-identification procedure.

Each reference has its published properties, uses and settings. Their sheets do not fully detail every reinforcement's composition or separate the polymer effect from the reinforcement effect. Keep those limits when comparing values. The PETG guide gives general context for that material without replacing the conditions for the two Fiberon references examined here.

Before buying, read the full grade name and its datasheet. A listed Tg, melting temperature or “N/A” helps explain what the manufacturer reports for that product; it does not, by itself, authenticate a spool. If the packaging, product page and datasheet disagree, ask the manufacturer or seller to confirm the exact grade.

Read the grade name before comparing two sheets

The documents identify two grades: PET-CF17 and PETG-rCF08. The second specifies recycled carbon fiber. A name and its code digits alone do not detail fiber mass fraction, length or complete source; these TDS documents do not supply all that information here. Record the reinforcement actually described and preserve missing fields before assigning a property difference to fiber content alone. The grade code identifies the product rather than independently measuring its composition.

That matters when you compare stiffness or strength. You are comparing the polymer and the reinforcement at the same time, and blaming the whole gap on PET versus PETG would be a misreading. The carbon fiber filament guide covers how much fiber content and fiber type move the modulus.

PET-CF17's mechanical section states that all its specimens were annealed at 120°C for ten hours. The PETG-rCF08 TDS gives N/A in the annealing entry without reporting equivalent preparation here. That does not prove an unannealed state: the information must remain unreported. The cited standards alone therefore do not establish identical preparation for the two sets of results. Record this distinction alongside the measurements rather than filling the gap from an assumption.

Heat: what Tg, HDT and Vicat actually tell you

For these two grades, the datasheets list different typical values: Fiberon PET-CF17 reports Tg 79.3 °C, HDT 105 °C at 1.8 MPa and 147.5 °C at 0.45 MPa, and Vicat 238.4 °C; PETG-rCF08 reports Tg 69.7 °C, HDT 65.7 °C and 68.6 °C at the same loads, and Vicat 81.6 °C. PET-CF17 states that all specimens were annealed at 120 °C/10 h; PETG-rCF08 does not report that preparation. These test values are not service temperatures or a universal mechanical or thermal ranking.

These are typical values measured on specimens under each sheet's own conditions, including the anneal for PET-CF17. They are meant for comparison between materials, not for designing a part. Polymaker's own disclaimer says actual values vary significantly with printing conditions, part design, and environment.

Tg, HDT and Vicat are different tests; none of those rows alone gives an allowable use temperature for a part. In a datasheet comparison, keep the HDT load and specimen state with each value. For a design, identify the relevant load, duration and environment; these two sheets do not validate a particular use.

Moisture: two very different drying instructions

Both datasheets label their curves at 70% RH and 23 °C, reporting 0.53% for PET-CF17 and 0.55% for PETG-rCF08 at equilibrium. They also give different drying instructions for these references: 100 °C/10 h and 65 °C/3 h. Treat these as product-specific instructions, not a comparative measure of drying ease or general polymer sensitivity.

The PET-CF17 datasheet uses the phrase “moisture insensitivity” for that grade; the PETG-rCF08 sheet says that grade is moisture-sensitive and calls for storage and use below 20% RH. These are manufacturer statements about the exact products. They do not establish that a polymer family is moisture-insensitive or replace the curve values and conditions.

Compare the specified drying temperature with your equipment’s published range and the exact product instructions; neither sheet evaluates consumer dryer performance or a substitute method. The storage-humidity ceiling applies to PETG-rCF08 per Polymaker; it does not establish that a hygrometer or dry box will guarantee that value.

Print settings: nozzle, bed, cooling and annealing

The recommended printing conditions confirm the split. For PET-CF17, Polymaker lists a nozzle range of 270 to 300 °C, a bed of 70 to 80 °C, a room-temperature chamber, the cooling fan off, and speeds up to 300 mm/s. For PETG-rCF08, the sheet lists a nozzle range of 240 to 270 °C, a bed of 60 to 70 °C, cooling at 0 to 50 %, and the same top speed.

Compare your printer’s published maximum temperature with the exact grade’s range. The PET-CF17 sheet lists 270–300 °C at the nozzle; it does not say that every machine can hold 300 °C continuously. Its test values are the sheet’s conditions, not validation of a particular hotend’s compatibility.

The PETG-rCF08 TDS reports frequent brass abrasion and estimates typical life around nine hours. It highly recommends a wear-resistant nozzle such as hardened steel or ruby. The PET-CF17 TDS does not contain that same nozzle-material note; this omission means neither absence of wear nor compatibility with every setup. Obtain guidance for that reference from the manufacturer. Its 120°C/ten-hour anneal is strongly recommended with several precautions in the complete sheet.

Mechanical numbers: why they do not rank cleanly

Both sheets cite ISO 527, ISO 178 and ISO 179, but their mechanical values are not directly equivalent: PET-CF17 specimens were annealed at 120 °C/10 h; the PETG-rCF08 sheet does not report annealed specimens. References and print conditions also differ, and their composition is not fully detailed here. Keep those differences with the results; a shared standard alone does not rank parts.

The X-Y values in the datasheets belong to specimens prepared under each document’s conditions: PET-CF17 lists a 5481 MPa modulus, 65.9 MPa tensile strength and 2.4% elongation; PETG-rCF08 lists 3710.1 MPa, 59.8 MPa and 5.7%, respectively. The sheets report Z results separately. Do not turn them into a “stiffer” or “stronger” verdict without comparable method, orientation, load and specimen state.

The sheets do not justify summarizing the grades as “stiffer and brittle” versus “more ductile”: the values come from different formulations, orientations and specimen states. None is a design specification; according to the manufacturers’ disclaimers, a part’s performance also depends on geometry, printing and environment.

What to check before you order

Start by checking the exact product name and its manufacturer documentation. A melting temperature or “N/A” describes what the datasheet reports; it is not, by itself, a filament identification test. Then compare nozzle and drying ranges with the documentation for your printer and equipment. If you cannot reproduce the published conditions, do not assume the typical values transfer to your print.

Read each HDT with its test load and specimen conditioning; neither figure alone gives an allowable use temperature. A choice depends on the documented requirements of the part and relevant tests. These sheets do not establish that a grade is easier to print or suitable just because a part operates at room temperature. The PCTG vs PETG page covers a different comparison.

The wear-resistant nozzle recommendation here explicitly applies to Fiberon PETG-rCF08; the PET-CF17 passages cited do not specify nozzle material. For moisture, use each grade’s published drying and storage conditions. The sheets do not compare accessory and spool costs; the startup budget tool lets you enter your own costs without implying a comparison from these sheets.

Sources and limits

• Polymaker Fiberon — PET-CF17 technical data sheet V1.0
• Polymaker Fiberon — PETG-rCF08 technical data sheet V1.0

We organize manufacturer and community documentation; we have not measured these products ourselves. The manual for your exact model takes precedence over general guidance.