PETG (Glycol-modified Polyethylene Terephthalate) for FDM

Material Profile: PETG (Glycol-modified Polyethylene Terephthalate) for FDM

FDM Engineering Material Technical Report Series

Compiled from manufacturer technical datasheets and peer-reviewed literature

Abstract—PETG is the 'middle ground' between PLA's printability and ABS's mechanical performance. The glycol modification (cyclohexanedimethanol replacing some ethylene glycol units in the PET backbone) suppresses crystallisation, yielding a clear amorphous polymer that prints without warping, exhibits high impact resistance, and is approved for food-contact applications in many grades. PETG is widely used for end-use mechanical parts, transparent enclosures, drinkware, and outdoor brackets.

Index Terms—additive manufacturing, FDM, PETG, polyester, food-contact, transparent, general-purpose filament.

I.  MATERIAL IDENTIFICATION

This section establishes the canonical names and commercial designations under which the material is supplied.

A.  Designation

Trade name: PETG (generic). Commercial grades include Polymaker PolyLite™ PETG, Prusament PETG, Bambu Lab PETG HF / PETG-CF, eSUN PETG, BASF Ultrafuse PET / PETG. Eastman Chemical Company's Eastar™ resin is a common base.

B.  Full Chemical Name

Glycol-modified poly(ethylene terephthalate) — copolyester of terephthalic acid with a mixture of ethylene glycol (EG) and 1,4-cyclohexanedimethanol (CHDM). The CHDM substitution (typically 30–40 mol%) disrupts crystallinity, giving an amorphous transparent polymer.

C.  Aliases and Alternative Designations

II.  COMPOSITION AND MOLECULAR STRUCTURE

A.  Empirical Chemical Formula

Idealised: [-O-CH₂-CH₂-O-CO-C₆H₄-CO-]ₙ with ~30% of the ethylene glycol replaced by 1,4-cyclohexanedimethanol [-O-CH₂-C₆H₁₀-CH₂-O-]; empirical (C₁₀H₈O₄)ₙ for the PET portion.

Fig. 1.  Repeating unit / structural schematic of the polymer matrix.

Fig. 2.  Schematic of the single-phase polymer (no reinforcement).

B.  Composition Breakdown

TABLE I
 COMPOSITIONAL BREAKDOWN OF PETG (TYPICAL / PER SUPPLIER DATASHEET)

III.  MECHANICAL PROPERTIES — XZ PRINT DIRECTION

In the XZ orientation the tensile load is applied parallel to the deposited rasters; for fibre-reinforced grades this is the strongest orientation because the fibres align preferentially along the extrusion direction.

TABLE II
 MECHANICAL PROPERTIES — XZ ORIENTATION (PETG)

IV.  MECHANICAL PROPERTIES — ZX PRINT DIRECTION

In the ZX orientation the tensile load is applied perpendicular to the print layers, so failure occurs through inter-layer (Z) bonds. Properties are markedly lower than in XZ — this anisotropy is intrinsic to FDM.

TABLE III
 MECHANICAL PROPERTIES — ZX ORIENTATION (PETG)

XZ:ZX UTS ratio ≈ 1.3:1 — PETG's amorphous nature and good melt re-flow give excellent layer adhesion, among the best of any standard FDM material. Strings and oozing during print, however, are common problems requiring careful retraction tuning.

V.  RECOMMENDED PRINT PARAMETERS

Values summarised below give consensus operating windows from public datasheets. Specific suppliers may differ within ±10 °C; the supplier datasheet always supersedes this table.

TABLE IV
 RECOMMENDED PRINT TEMPERATURE RANGES FOR PETG

XZ:ZX UTS ratio ≈ 1.3:1 — PETG's amorphous nature and good melt re-flow give excellent layer adhesion, among the best of any standard FDM material. Strings and oozing during print, however, are common problems requiring careful retraction tuning.

V.  RECOMMENDED PRINT PARAMETERS

Values summarised below give consensus operating windows from public datasheets. Specific suppliers may differ within ±10 °C; the supplier datasheet always supersedes this table.

TABLE IV
 RECOMMENDED PRINT TEMPERATURE RANGES FOR PETG

VI.  GLASS TRANSITION TEMPERATURE (TG)

Reported / typical Tg: ≈ 80–85 °C.

PETG's amorphous nature means it has only a glass transition (no melting point in the conventional sense) — softening is gradual above Tg. Service temperature is generally limited to 65–70 °C continuous to avoid creep. PETG cannot be annealed productively (no crystallinity to develop).

VII.  HEAT DEFLECTION TEMPERATURE (HDT)

Heat deflection temperature is the temperature at which a standard bar deflects 0.25 mm under a specified flexural load (ASTM D648 / ISO 75).

TABLE V
 HEAT DEFLECTION TEMPERATURE OF PETG UNDER STANDARD TEST LOADS

VIII.  DISTINGUISHING CHARACTERISTICS AND STANDARDS

A.  Food-contact compatibility (in select grades)

Many PETG grades use FDA 21 CFR 177.1660-compliant Eastman Eastar resin and are advertised as 'food-safe'. Important caveats: (1) the FDA approval is for the resin in its bulk form, not a 3D-printed part — porosity from layer lines harbours bacteria, making washing difficult; (2) brass nozzles can leach lead; (3) any additives or colorants must also be food-grade. Direct food contact applications should specify a food-grade filament and use a stainless-steel nozzle with appropriate post-processing.

B.  Optical clarity

Amorphous PETG can be printed with > 80% light transmission in transparent grades, useful for fluid visualisation, light-pipes, and decorative applications. Layer lines remain visible — true optical-grade clarity requires post-print polishing or solvent vapour smoothing.

C.  Chemical resistance

PETG resists most aqueous solutions, dilute acids and bases, oils, alcohols, and petroleum products. Attacked by ketones (acetone, MEK), strong bases, and aromatic / chlorinated solvents.

D.  Impact toughness without printing difficulty

PETG offers 3–5× the notched impact strength of PLA while requiring no enclosure or heated chamber — making it the typical choice for end-use mechanical parts on consumer-class printers. Hinges, snap-fits, and parts subject to drop impact perform substantially better than PLA equivalents.

IX.  REPRESENTATIVE APPLICATIONS

PETG is typically deployed in the following applications:

1)  Mechanical functional parts: Brackets, mounts, snap-fits, drone frames where impact resistance matters more than thermal capability.

(Source : Incept3d)

2)  Transparent enclosures and light pipes: Display covers, fluid sight glasses, decorative LED housings.

3)  Food-contact items (with caveats): Custom drinkware, cookie cutters, bottles — requires food-grade filament and proper post-processing.

(Source : Reddit)

4)  Outdoor brackets and signage: Better UV stability than PLA; not as good as ASA but usable for medium-term outdoor service.

5)  Medical / lab equipment housings: Sterilizable (chemical / EtO); transparent; impact-resistant.

X.  REFERENCES

[1]  Polymaker, “PolyLite™ PETG Material Data Sheet,” 2024. Available: https://us.polymaker.com/products/polylite-petg

[2]  Prusa Research, “Prusament PETG Material Data Sheet,” 2024. Available: https://prusament.com/materials/prusament-petg/

[3]  Eastman Chemical Co., “Eastar™ Copolyester EN001,” technical literature.

[4]  FDA, 21 CFR § 177.1660, “Polyester resins, cross-linked,” U.S. Food and Drug Administration.

[5]  S. Latko-Durałek et al., “Mechanical properties of PETG 3D-printed structures,” Materials, 2019.

[6]  ASTM D638-14; ASTM D256-10; ASTM D648-18.