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FDM Part III Polyester Family
FDM Polymers — A Technical Reference ›
The polyester family in FDM: PETG and PCTG, the glycol-modified copolyesters that dominate functional printing, and PET with its reinforced PET-CF and PET-GF grades.
PETG (polyethylene terephthalate glycol-modified) is the workhorse functional filament: easier to print than ABS, tougher than PLA, chemically resistant to a wider range of solvents than either, and available from essentially every filament manufacturer at $15–25/kg. The copolyester family extends beyond strict PETG into marketed-as-CPE, nGen, AthenaX, and t-glase variants · all chemically related, all amorphous glycol-modified copolyesters.
PETG is polyethylene terephthalate (PET) with a fraction of the ethylene glycol replaced by 1,4-cyclohexanedimethanol (CHDM). When CHDM is less than 50 mol% of the diol fraction, the polymer is called PETG; the CHDM disrupts crystalline packing enough to keep the polymer amorphous (no melt-driven crystallization, no Schlieren texture, full optical transparency in clear grades) while leaving the PET-class tensile envelope intact. Eastman (Eastar, Amphora) and SK Chemicals (Skygreen) are the major branded base resins, with Skygreen probably the largest by filament volume; unbranded copolyesters fill the lower price tier.
| Property | Typical PETG | Notes |
|---|---|---|
| Density (g/cm3) | 1.23–1.27 | Pigment-dependent |
| Tg(°C) | 75–80 | Service ceiling (amorphous; annealing does not raise it) |
| Tm(°C) | n/a | No true Tm - amorphous; print 230-250 |
| HDT @ 0.45 MPa (°C) | 70–75 | Filament-form value |
| Tensile strength @ yield (MPa) | 40–50 | ISO 527, XY |
| Tensile modulus (GPa) | 1.9–2.1 | |
| Elongation @ break (%) | 8–25 | Brand-dependent; tough grades higher |
| Notched Izod (kJ/m2) | 4–8 | About 2× PLA |
| Saturated moisture absorption (%) | 0.2–0.4 | Cosmetic effect on prints |
| Optical clarity | good | Clear grades 85–90% transmittance |
| UV stability | moderate | Months outdoor; pigments help |
Table 7.1 — PETG typical property envelope. Brand-to-brand variation is approximately ±15% on tensile and ±50% on elongation.
Nozzle 230–250 °C (some impact-modified grades up to 260 °C), bed 80–90 °C, part cooling 30–60% (lower than PLA, higher than ABS), brim recommended for parts over 60 mm in longest dimension. Pressure advance bracket typically 0.030–0.060. Max volumetric flow 10–14 mm3/s on standard hotends. PETG is sticky in melt and tends to over-adhere to smooth PEI: glue stick on glass, or PVP coating, or accept reduced bed temperature on textured PEI to prevent sheet damage on part removal.
Tough PETG / PETG+ / co-PETG: impact-modified grades from Polymaker (PolyMax PETG), Fiberlogy, and others; elongation pushed to 100%+ at modest tensile sacrifice. PolyMax PETG in particular approaches PCTG behavior without being labeled as such; the high-CHDM characterization is an inference from its property envelope, as Polymaker's current public documentation does not disclose the CHDM content. nGen, CPE, CPE+ (Amphora-based): Eastman Amphora copolyester grades marketed under various proprietary names; functionally similar to PETG with slightly higher Tg and toughness. t-glase, PETT: Taulman's high-clarity copolyester; sold as “100% recyclable” though local infrastructure rarely supports it. AthenaX (FormFutura): positioned in the FormFutura X-line as a step above ApolloX (ASA) and TitanX (ABS); FormFutura identifies it as PCTG (AthenaX GF10 is PCTG + 10% glass fiber), and the property envelope matches.
PETG is the right choice for: functional prototypes that need toughness PLA lacks, parts that see occasional bumps but not sustained impact, transparent enclosures (in clear grades), indoor mechanical parts that see service up to 60 °C, parts requiring food-contact compatibility at the resin level (not the printed surface). It is not the right choice for: parts that see repeated drops or impact loading (use PCTG or PC blend), parts above 70 °C service (Tg ceiling), outdoor UV exposure exceeding a few months (use ASA), or precision-fit assemblies where the higher moisture sensitivity and shrinkage variability matter.
PCTG occupies a useful niche between PETG and PC. The headline mechanical signature is a two-to-three-fold improvement in printed notched impact strength over PETG — typical Izod values of 8-24 kJ/m2 vs PETG's 4-8 kJ/m2 while sharing the same processing envelope; the order-of-magnitude gap (≈93 vs ≈7 kJ/m2) is a molded-resin figure that printed parts do not realize. Where PETG loses energy to crack propagation, PCTG absorbs it in plastic deformation. The cost is a $10–15/kg premium over PETG and (more importantly) the fact that not every spool marketed as “PCTG” uses the same base resin.
PCTG is built on the same TPA + glycol-mix backbone as PETG, but with CHDM above 50 mol% of the diol fraction. The dominant CHDM raises Tg modestly (85–95 °C vs PETG's 75–80), eliminates crystallinity completely (full transparency, no Schlieren scattering), and produces the notched-impact toughness step-up. One diacid (TPA) and three diols define the compositional space:
| Monomer | Role in the polymer | Effect when dominant |
|---|---|---|
| Terephthalic acid (TPA) | Aromatic diacid backbone | Stiffness, UV absorption, hydrolytic anchor |
| Ethylene glycol (EG) | Linear short diol | Promotes crystallinity; PET-like packing |
| 1,4-cyclohexanedimethanol (CHDM) | Bulky cycloaliphatic diol | Disrupts crystallinity; raises Tg and toughness |
| 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCD) | Rigid cyclic diol; Tritan-specific | Further raises Tg; improves hydrolytic stability |
Table 8.1 — The compositional building blocks of the PETG–PCTG–Tritan family.
Eastman Tritan (the resin behind most premium “PCTG” filaments) is technically a terpolymer of TPA + CHDM + TMCD — not strictly PCTG. The TMCD ring lifts Tg and hydrolytic stability beyond what TPA + CHDM alone produces, which is why Eastman markets Tritan as a polycarbonate substitute in dishware applications. Filaments built on Tritan-class resins (3D-Fuel Pro PCTG, the legacy Essentium PCTG, some Spectrum and Fiberlogy grades) should be expected to outperform pure TPA-CHDM PCTG on the temperature and hydrolysis axes; the converse is that not every filament sold as “PCTG” is the same polymer. The filament TDS rarely identifies the underlying resin grade.
The values below are from the Eastman TX1001 TDS. These are test-bar values, not printed-part values; printed mechanical envelope runs 10–30% below the tensile and modulus numbers here, with notched Izod the most sensitive to layer-bonding quality.
| Property | Method | Value |
|---|---|---|
| Specific gravity | ASTM D792 | 1.18 |
| Tensile stress @ yield (MPa) | ISO 527 | 43 |
| Tensile strength @ break (MPa) | ISO 527 | 58 |
| Elongation @ break (%) | ISO 527 | 185 |
| Tensile modulus (MPa) | ISO 527 | 1,548 |
| Flexural modulus (MPa) | ISO 178 | 1,495 |
| Flexural strength (MPa) | ISO 178 | 59 |
| Izod, notched @ 23 °C (kJ/m2) | ISO 180 | 93 |
| Izod, notched @ -40 °C (kJ/m2) | ISO 180 | 20 |
| Rockwell hardness (R scale) | ASTM D785 | 112 |
| Total light transmittance (%) | ASTM D1003 | 90 |
| Haze (%) | ASTM D1003 | <1 |
| HDT @ 0.455 MPa (°C) | ASTM D648 | 99 |
| HDT @ 1.82 MPa (°C) | ASTM D648 | 85 |
| Mold shrinkage (in/in) | ASTM D955 | 0.005–0.007 |
| Drying schedule | — | 88 °C, 4–6 h |
| Melt processing range (°C) | — | 260–282 |
Table 8.2 — Eastman Tritan TX1001 resin TDS. Note the gap between resin HDT (99 °C) and typical filament HDT (~76 °C) — primarily a base-resin difference (generic CHDM-rich copolyester ~76 °C vs TMCD-containing Tritan 99 °C), compounded by printability-tuned additive packages; see Table 8.3.
| Property | Spectrum Premium | Fiberlogy PCTG | FormFutura AthenaX | Tritan TX1001 (resin) |
|---|---|---|---|---|
| Density (g/cm3) | 1.23 | ~1.23 | ~1.23 | 1.18 |
| Tensile @ yield (MPa) | 44 | — | 44 | 43 |
| Tensile @ break (MPa) | 46 | — | 44 | 58 |
| Elongation @ break (%) | 220 | — | 220 | 185 |
| Flexural strength (MPa) | 60 | — | — | 59 |
| Flexural modulus (MPa) | 1,600 | — | — | 1,495 |
| **Notched Izod (kJ/m2) *** | 93 | ~90 | — | 93 |
| HDT @ 0.455 MPa (°C) | 76 | 76 | — | 99 |
| HDT @ 1.82 MPa (°C) | 64 | — | — | 85 |
| Vicat softening (°C) | 88 | — | — | — |
| Rockwell R hardness | 105 | — | — | 112 |
Table 8.3 — PCTG filament property envelope by brand. Dashes indicate values not published. The filament-vs-resin HDT gap most plausibly reflects base-resin choice (generic CHDM-rich PCTG HDT ~76 °C vs TMCD-containing Tritan 99 °C) plus printability-tuned additive packages; HDT is modulus-governed and largely insensitive to layer-bond quality. * Notched-Izod figures are resin-basis TDS values; printed PCTG specimens run far lower.
PCTG is moderately polar and resistant to most non-polar solvents, dilute mineral acids, salt solutions, and aliphatic oils. It is attacked by strong bases, concentrated mineral acids, ketones (acetone, MEK), chlorinated solvents (DCM, chloroform), and many aromatic solvents (toluene, xylene). The CHDM/TMCD-rich backbone gives PCTG a real step up over PETG against acids, alcohols, and detergents — 3D-Fuel publishes chemical-resistance ratio (CRR) data claiming 1.5–2× PCTG advantage over PETG across most cleaner and oil exposures.
| Class | Examples | PCTG behavior |
|---|---|---|
| Mineral acids, dilute | 10% HCl, 10% H2SO4 | Resistant; no swelling at RT |
| Mineral acids, conc. | Conc. HCl, HNO3, H2SO4 | Attacked; ester hydrolysis at elevated T |
| Strong bases | NaOH, KOH | Slow saponification; avoid chronic exposure |
| Aliphatic hydrocarbons | Hexane, mineral oil, kerosene | Resistant |
| Alcohols | IPA, ethanol, methanol | Resistant; cosmetic crazing under load |
| Ketones | Acetone, MEK | Attacked; softening, crazing, dissolution |
| Esters | Ethyl acetate, butyl acetate | Attacked; not useful for vapor smoothing |
| Chlorinated solvents | DCM, chloroform, TCE | Strongly attacked; lab handling only |
| Aromatic solvents | Toluene, xylene | Attacked; surface softening |
| Aqueous detergents | Dishwasher cycles | Excellent (Tritan target application) |
| Fuels | Gasoline, diesel | Marginal; both PETG/PCTG swell over time |
| UV exposure | Outdoor sun | Better than PLA/PETG; pigment-dependent |
Table 8.4 — PCTG chemical compatibility. Tritan-class grades carry hydrolytic-stability marketing claims supported by Eastman's dishwasher test data.
| Brand | Product | $/kg | Notable |
|---|---|---|---|
| 3D-Fuel | Pro PCTG | ~30 | Tritan-based; broad colors; ReFuel (regrind) variant |
| Spectrum | Premium PCTG | ~25 | Well-documented TDS; full CF and GF variants |
| Fiberlogy | PCTG | ~30 | Pure TR (food-contact) clear; CF and GF variants |
| FormFutura | AthenaX | ~30 | Positioned in X-line alongside ApolloX (ASA), TitanX (ABS) |
| Essentium / Vision Miner | PCTG | ~45 | Legacy listing: Essentium exited filament production in the Nexa3D restructuring; 3D-Fuel took over its PCTG line |
| American Filament | PCTG | ~25 | US; food-contact clear and basic colors |
| Nobufil | PCTG | ~30 | Austrian; smaller catalog; color-focused |
| Tangled Filament | PCTG (preorder) | ~22 | Aggressive price target ($13/kg eventual) |
| Polymaker | PolyMax PETG | ~22 | Marketed as PETG; property envelope near PCTG; CHDM content undisclosed |
Table 8.5 — PCTG brand landscape (early 2026). Prices are typical 1 kg / 1.75 mm retail, expect ±15% drift. Polymaker PolyMax PETG is included because its property envelope sits adjacent to PCTG; the high-CHDM reading is inference from behavior rather than a Polymaker disclosure, and the product is nominally still PETG.
PCTG-CF (typically 10% chopped CF). Reference values from Spectrum PCTG CF10: tensile yield 70 MPa (+59% vs the same vendor's unfilled PCTG), elongation @ break 5% (-98% on that same comparison basis), notched Izod 4 kJ/m2, HDT @ 0.455 MPa 78 °C (+3%). Because impact data is strongly test-method and specimen-basis dependent, compare the CF and unfilled grades only against the same vendor's TDS or an identical printed-coupon test. The CF gives strength and stiffness but trades away the headline impact toughness; PCTG-CF behaves more like PETG-CF or short-fiber nylon than unfilled PCTG. Use for stiff, dimensionally stable fixtures and brackets, not impact-loaded parts. Hardened nozzle mandatory.
PCTG-GF (typically 10% GF). Similar trade as CF, slightly less stiff, lighter color (white/translucent matte). 3D-Fuel, Spectrum, and Fiberlogy offer 10% GF grades. Processing window matches CF closely. Aggressive drying because fiber surface area increases moisture uptake.
Tritan-based grades. Where a vendor specifies Tritan resin (or the property envelope strongly implies it: notched Izod >15 kJ/m2, HDT >80 °C, <1% haze), expect better dishwasher/hot-fluid behavior, marginally better UV, and a small ($3-7/kg) price premium. For repeatable food-contact or medical-adjacent work, Tritan-based PCTG is the defensible choice.
Recycled / ReFuel. 3D-Fuel's ReFuel Pro PCTG is built from regrind. Mechanical envelope is essentially indistinguishable from virgin Pro PCTG on tensile and impact; color is not selectable — the mixed reclaim feedstock yields a variable tone from gray-white to near-black that shifts batch to batch — and diameter tolerance is the same ±0.02 mm. Useful for jigs and prototyping where the recycled story matters and color flexibility doesn't.
| Parameter | Range | Notes |
|---|---|---|
| Nozzle (°C) | 250–280 | Vendors split: Spectrum 250–270; 3D-Fuel 260–280; Fiberlogy 250–270 |
| Bed (°C) | 70–90 | PEI smooth/textured; glue stick on glass; PVP coating |
| Chamber | open or passively warm | No active heating required |
| Part cooling fan (%) | 30–60 | Lower than PLA, higher than ABS; 100% acceptable on small features |
| Print speed (mm/s) | 40–80 body / 30–50 wall | High melt strength tolerates fast moves; stringing increases |
| Max volumetric flow (mm3/s) | 8–12 | 20+ on high-flow hotends (CHT, Bambu HF); always calibrate |
| Retraction (direct drive) | 0.6–1.2 mm @ 30–45 mm/s | |
| Retraction (Bowden) | 3–6 mm @ 30–45 mm/s | |
| Pressure advance | 0.03–0.06 | 3D-Fuel Pro PCTG calibrated at 0.053 in author's testing (see Appendix B) |
| XY shrinkage compensation | 0.2–0.5% | User reports of 2–2.5% scaling are inconsistent with amorphous shrinkage physics; likely calibration error (over-extrusion, hole compensation), not material shrinkage |
| Drying | 65–70 °C, 4–6 h | Required for transparent prints; resin TDS spec is 88 °C |
Table 8.6 — PCTG starting print parameters (0.4 mm nozzle). Per-spool calibration mandatory; the Spectrum-vs-3D-Fuel temperature split reflects real composition differences.
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Avoid grid infill. Grid lines cross within the same layer, dragging the nozzle through extruded material twice and depositing PCTG on the nozzle until it eventually drops onto the part. 3D-Fuel's published process profiles override the typical slicer default to cubic or gyroid for exactly this reason.
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Disable avoid_crossing_perimeters when it produces artifacts. Some PCTG/PETG users have reported travel-path artifacts in recent slicer builds when this option is enabled; because the behavior is version- and model-specific, treat this as a troubleshooting switch rather than a universal rule.
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Watch top-surface dishing. On low-density sparse infill (≤15%) thin top surfaces can pull down between infill lines as PCTG cools — same mechanism as the PP-CF dishing issue in §11.6, just less severe. Use 6–8 top layers, 20–25% cubic infill, or both.
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Multi-material with PETG and PLA. PCTG bonds well to PETG; pair freely in multi-material prints. PCTG bonds poorly to PLA — useful as a release interface for PLA supports, deliberately. Purge volumes between PCTG and PETG can be lower than the typical slicer default.
Choose PCTG when: impact loading or drop survival matters (tool housings, drone bodies, RC parts, lab equipment); ductile failure mode is required (living hinges, snap-fits with more than a few cycles, clips, latches); optical clarity matters (light pipes, transparent enclosures, fluid sight glasses, optical mockups — transmittance comparable to PETG clear, with lower haze (<1%) in Tritan-class grades); food and drinking-water contact at the resin level (Tritan carries FDA 21 CFR food-contact compliance and NSF/ANSI 51/61 at the resin level, verify per-filament additives); cold-weather toughness (PCTG retains useful notched Izod at -40 °C where PETG embrittles).
Do not choose PCTG when: heat above ~80 °C is in scope (use PC, PC-CF, ASA, or PPA); long-term outdoor UV (use ASA); wear surfaces under sliding load (use POM, PEEK, or iglidur); solvent smoothing is part of the workflow (no common workshop solvent works on PCTG); lowest-cost prototyping (PETG saves $10–20/kg with comparable printability).
| Method | PCTG suitability | Notes |
|---|---|---|
| Sanding (dry/wet) | Good | Wet sand 320 -> 800 -> 1500 for matte; keep moving, keep wet |
| Mechanical polishing | Good | After 2000 grit, plastic polish or buffing for near-transparent on clear grades |
| Acetone vapor smoothing | Not effective | Attacks but doesn't flow; produces degraded matte surface |
| Ethyl acetate vapor smoothing | Marginal | Better than acetone; PCTG response is inconsistent |
| MEK or DCM smoothing | Possible / hazardous | DCM dissolves; both require fume hood |
| Heat-gun smoothing | Possible | Brief distant passes melt a thin surface skin; easy to overshoot |
| 2K epoxy coating (XTC-3D) | Excellent | Reliable smooth surface; adds layer thickness |
| Painting | Good | Sand to 320; plastic-bonding primer (SEM, Bulldog); then topcoat |
| Annealing | Limited gain | Amorphous; no crystallization; small stress-relief gain |
| Threading / tapping | Excellent | Ductility holds threads better than PETG |
| Gluing | Good | CA for fast; Loctite Plastic Bonder for structural |
Table 8.7 — Post-processing options for PCTG. The chemical resistance that makes PCTG service-friendly also limits the solvent-smoothing workflow.
Resin identity is rarely disclosed. Most filament TDSs identify the material as “PCTG” without naming the resin. Whether any given spool is Tritan, generic Eastman PCTG (Eastar series), SK Skygreen or a Chinese copolyester materially affects performance — and is generally only inferable from price and property envelope.
Z-direction values are largely unpublished. Vendors publish XY tensile and Izod; Z values can be 15–40% lower. Engineering design requires bracket testing on the actual machine.
UV field-life data is sparse. “UV resistant” on a TDS rarely comes with hours of QUV exposure or color-shift data. Outdoor service life claims should be tested, not trusted.
Food-contact compliance does not transfer to printed parts. Resin certifications (FDA 21 CFR, NSF 51, NSF 61) apply to the resin as molded. FDM layer lines harbor bacteria and contamination from hotend residues; for repeated-use food contact, coat or seal. Filament-level certifications typically cover the resin plus additives — not the printed surface.
Independent third-party test coverage of PCTG remains thin relative to PLA and PETG. Cross-brand impact and tensile comparisons under uniform print conditions remain the largest open empirical gap for this material.
Polyethylene terephthalate is the parent polyester of the family this Part covers: PETG and PCTG are both glycol-modified descendants of PET, engineered specifically to defeat the property that makes unmodified PET awkward to print. That makes PET worth a chapter of its own — not because plain PET filament is common (it is not), but because understanding why it is uncommon explains the entire copolyester category, and because the two reinforced grades that are printable in practice, PET-CF and PET-GF, behave unlike anything else in Part III.
PET is the condensation polymer of terephthalic acid (TPA) and ethylene glycol (EG) — a rigid aromatic diacid joined to a short, regular two-carbon diol. The regularity is the point: an unbranched, symmetric backbone packs readily into crystalline domains. PET is therefore a strongly semi-crystalline polymer, with a melting transition near 250–260 °C and a glass transition near 70–80 °C. In its crystalline form it is the material of drink bottles, polyester fiber, and thermoformed packaging — strong, stiff, chemically durable, and inexpensive at industrial scale.
That same crystallinity is what makes PET difficult as an FDM feedstock. A polymer that crystallizes readily also crystallizes unevenly during the rapid, directional cooling of fused-filament deposition: crystalline and amorphous regions form at different rates in different parts of the bead, they have different densities, and the resulting differential shrinkage drives warping, poor layer registration, and opacity. PETG and PCTG exist to solve exactly this. Substituting some of the ethylene glycol with the bulky, ring-shaped cyclohexanedimethanol (CHDM) disrupts the backbone regularity enough that the polymer can no longer crystallize on FDM timescales — it stays amorphous, prints predictably, and finishes clear. PETG is the glycol-modified grade; PCTG is the higher-CHDM grade with greater toughness. Both trade PET's crystalline stiffness and temperature resistance for printability.
One point of vocabulary is worth settling here, because it causes recurring confusion. PLA is also a polyester — Part II covers it as its own family — so a reader is entitled to ask why it is not simply folded into this Part. The answer is that “polyester” names a bond, not a behavior: any polymer whose backbone is built from ester linkages qualifies. PET, PETG, and PCTG are aromatic copolyesters — their stiffness and thermal resistance come from the benzene ring in the terephthalic-acid unit. PLA is an aliphatic polyester, built from lactic-acid units with no aromatic ring at all. That single structural difference cascades into everything a practitioner cares about: PLA is bio-derived, prints cold, barely warps, and softens well below 60 °C, whereas the aromatic PET family prints hot, is hygroscopic, and holds its shape far higher. Grouping by printing behavior — PLA in Part II, the aromatic copolyesters in Part III — is therefore more useful to the reader than grouping by the shared ester bond, even though the latter is the stricter chemical taxonomy.
Unmodified PET is sold as filament only rarely, and it is worth being explicit about why rather than treating it as a routine option. Three factors compound. First, the crystallization behavior above: a part can warp, delaminate, or finish cloudy depending on cooling history, and the cooling history is hard to control across a whole print. Second, PET is aggressively hygroscopic and must be printed dry — wet PET hydrolyses at melt temperature, and chain scission permanently lowers the molecular weight, so a poorly dried spool yields brittle parts no print setting can recover. Third, PETG already occupies the niche plain PET would fill: it is easier to print, nearly as strong, clearer, and costs no more. For an unreinforced polyester, there is little practical reason to choose PET over PETG, and the market reflects that. Where PET earns its place is reinforced — and there the calculus changes completely.
Adding chopped carbon fiber (PET-CF) or short glass fiber (PET-GF) to a PET matrix does something more useful than simply stiffening it. The fibers act as nucleation sites and as a physical brake on shrinkage: they give crystallization a controlled, distributed set of starting points and they mechanically restrain the matrix as it cools, so the differential-shrinkage warping that plagues unfilled PET is substantially suppressed. The reinforcement that is added for stiffness also happens to fix PET's core printability problem. The result is a pair of filaments that are stiffer and more dimensionally stable than PETG, with a usefully higher service temperature, and that print with far less drama than unfilled PET ever would.
PET-CF is the stiffer of the two and the lighter relative to PET-GF. Chopped carbon fiber raises modulus sharply; it also raises the compound's density slightly over the base resin, since carbon fiber is denser than PET — but the increase is far smaller than the glass-fiber equivalent, which is why PET-CF parts come out lighter than PET-GF parts of the same geometry. Parts are dark grey to black with a matte finish, dimensionally stable, and well suited to jigs, fixtures, and structural brackets where rigidity matters more than impact toughness. As with every carbon-filled filament, the trade is abrasion: a hardened or wear-resistant nozzle is mandatory, and the headline impact toughness drops well below that of unfilled PETG — PET-CF behaves like a stiff, brittle composite, not a ductile polymer. PET-GF trades some of that stiffness for a tougher, less brittle failure mode and a lower price; glass-filled parts are typically white or translucent-matte. Both grades are hygroscopic and fiber-reinforced filaments take up moisture faster than their base resin because the fiber–matrix interface offers additional surface area — drying is not optional.
| Property | PETG (reference) | PET-CF | PET-GF |
|---|---|---|---|
| Reinforcement | none (amorphous) | chopped carbon fiber | short glass fiber |
| Stiffness | baseline | much higher | higher |
| Impact toughness | high (ductile) | low (brittle composite) | moderate |
| Dimensional stability | good | excellent | excellent |
| Service temperature | baseline | higher than PETG | higher than PETG |
| Nozzle | brass acceptable | hardened mandatory | hardened mandatory |
| Typical appearance | clear / tinted | matte black / grey | white / matte |
Table 9.1 — Reinforced PET grades against PETG as the familiar reference point. The columns are qualitative by design: published datasheet values for PET-CF and PET-GF vary widely between vendors because fiber loading, fiber length, and base-resin grade are all uncontrolled variables, and a filament-level number is not portable between brands. Treat the table as a direction-of-effect guide and calibrate against the specific spool in hand.
The reinforced PET grades print hotter than PETG and demand the same discipline as any fiber-filled engineering filament: dry the spool, fit a hardened nozzle, and calibrate rather than trust the datasheet. The worked figures below are from a calibrated Fiberon PET-GF15 profile on a Core One with a 0.4 mm hardened (E3D Diamondback) nozzle, and are offered as a concrete, reproducible starting point rather than a universal specification — a different PET-GF spool, or a PET-CF grade, will need its own calibration pass.
| Parameter | Fiberon PET-GF15 (calibrated) | Notes |
|---|---|---|
| Nozzle temperature | 290 °C | hotter than PETG; the glass loading raises melt viscosity |
| Nozzle | 0.4 mm hardened (E3D Diamondback) | mandatory for any fiber-filled grade |
| Part cooling | fans off | cooling promotes uneven crystallization and weakens layer bonds |
| Extrusion multiplier | ~0.96 | calibrated by single-wall measurement, not assumed |
| Pressure advance | ~0.040 (starting value) | stored in the filament profile; tune per machine |
| Drying | mandatory before printing | fiber interface accelerates moisture uptake |
Table 9.2 — A calibrated PET-GF15 process profile (Core One, 0.4 mm hardened nozzle). The extrusion-multiplier and pressure-advance values are the result of the standard calibration workflow — temperature tower, volumetric-flow ceiling, extrusion multiplier by single-wall measurement, then pressure advance — not datasheet figures. Fans-off is deliberate: like the semi-crystalline engineering filaments, reinforced PET bonds layers better and warps less without part cooling.
Two process points carry over from the rest of Part III. Bed adhesion is straightforward — the polyester chemistry grips PEI well, as it does for PETG and PCTG — but the higher nozzle temperature and the absence of part cooling make a clean first layer and a stable chamber more important than they are for plain PETG. And the abrasion caution is not negotiable: a brass nozzle will measurably wear within a single large PET-CF or PET-GF print, after which extrusion consistency degrades.
Choose PET-CF when: the part is a jig, fixture, or structural bracket where stiffness and dimensional stability are the priority and impact loading is not; weight matters; and a hardened nozzle is available. Choose PET-GF when: the same stiffness-and-stability requirement applies but the part may see impact or handling stress, where PET-GF's less brittle failure mode is worth the modest loss of rigidity, and where cost is a consideration. Choose plain PETG or PCTG instead when: the part needs ductility, optical clarity, or food-contact compliance, or when a hardened nozzle is not available — the reinforced PET grades give up all of those. Reach past PET entirely when: the service temperature or chemical demands exceed what a reinforced polyester delivers, at which point the polyamide and polycarbonate families in the Parts that follow are the right place to look.
← Contents · ‹ Part II — PLA Family · Part IV — Styrenics Family ›
FDM Polymers — A Technical Reference
- Part I — Foundations
- Part II — PLA Family
- Part III — Polyester Family
- Part IV — Styrenics Family
- Part V — Polyolefins
- Part VI — Polyamides
- Part VII — Polycarbonates
- Part VIII — Thermoplastic elastomers
- Part IX — Specialty engineering thermoplastics
- Part X — High-temperature polymers
- Part XI — Support and niche polymers
- Part XII — Cross-cutting workflows
- Appendices
- Source manifest