Commodity Thermoplastic
PETG — Polyethylene Terephthalate Glycol
PETG is a glycol-modified variant of PET, offering excellent clarity, chemical resistance and impact strength. It is one of the most popular 3D printing filaments and is widely used in food packaging and medical devices.
Summary
PETG is a high-clarity, amorphous copolyester known for its exceptional toughness and ease of processing. Chemically modified with glycol to prevent crystallization, it offers the transparency of glass with significantly higher impact resistance than acrylic. It is a staple in medical packaging due to its sterilization compatibility and is the preferred material for complex thermoforming. While not UV stable or high-temperature resistant, its versatility across injection molding, extrusion, and 3D printing makes it an essential engineering thermoplastic for consumer goods and industrial components.
PETGPET-GEastarSpectarVivak
Manufacturers
3
Grades
4
Applications
6
Equivalents
3
Technical description
Polyethylene Terephthalate Glycol (PETG) is a clear, non-crystalline thermoplastic that belongs to the polyester family. It is produced by the modification of Polyethylene Terephthalate (PET) using 1,4-cyclohexanedimethanol (CHDM). This modification replaces some of the ethylene glycol in the polymer backbone, which effectively disrupts the molecular symmetry and prevents the material from crystallizing. The result is a permanently amorphous polymer that remains transparent even in very thick cross-sections, unlike standard PET which would turn opaque as it slowly cools and crystallizes.
Technically, PETG is characterized by a high glass transition temperature (Tg) of approximately 80°C (176°F) and a lack of a defined melting point, instead exhibiting a broad softening range. This makes it exceptionally suited for thermoforming, as it does not require the precise temperature control that crystalline polymers do. Its mechanical properties include a tensile strength of approximately 50 MPa and an Izod notched impact strength of about 80-100 J/m, making it much tougher than polystyrene or acrylic. It also possesses excellent chemical resistance against diluted acids, alkalis, and soaps, though it is vulnerable to certain solvents like esters and ketones.
From a processing standpoint, PETG is highly 'forgiving.' It has a low processing temperature (typically 220°C to 250°C) and demonstrates low mold shrinkage, usually between 0.2% and 0.5%. This dimensional stability is a key reason for its dominance in the 3D printing market. Furthermore, PETG does not require the same degree of intensive drying as polycarbonate or nylon. While it is hygroscopic, its moisture absorption rate is relatively slow, and it is less likely to undergo hydrolytic degradation during processing than many other polyesters, provided reasonable storage conditions are met.
History
The history of PETG is inextricably linked to the development of polyesters at Eastman Chemical Company. While PET was pioneered in the early 1940s by John Rex Whinfield and James Tennant Dickson for fibers (Dacron and Terylene), it was not until the 1970s that the modification of polyesters with glycols like 1,4-cyclohexanedimethanol (CHDM) became commercially significant. Eastman Chemical researchers identified that by substituting a portion of the ethylene glycol in the PET synthesis with CHDM, they could disrupt the polymer's ability to crystallize.
This breakthrough led to the commercialization of Eastar copolyesters in the late 1970s and 1980s. The material quickly gained traction in the packaging industry because it allowed for the production of thick-walled transparent containers that wouldn't turn hazy—a major limitation of standard PET. By the 1990s, PETG became the industry standard for medical device packaging due to its ability to be sterilized without losing its physical properties. In the 2010s, PETG saw a massive resurgence in popularity due to the rise of desktop FDM 3D printing, where it became the 'middle ground' material of choice between PLA and ABS.
Chemical structure
Polyethylene Terephthalate Glycol (PETG) is a non-crystalline copolyester, meaning it is an amorphous thermoplastic. It is synthesized by the polycondensation of terephthalic acid (TPA) or dimethyl terephthalate (DMT) with ethylene glycol (EG). The key distinguishing factor of PETG is the introduction of a second glycol, typically 1,4-cyclohexanedimethanol (CHDM), into the polymer chain. In a standard PET molecule, long chains of ethylene glycol and terephthalic acid tend to pack into crystalline structures when cooled slowly.
The CHDM molecules are much larger than the ethylene glycol units they replace. This structural irregularity prevents the polymer chains from neatly folding into crystalline lattices. Consequently, the material remains in a disordered, amorphous state even during slow cooling. This molecular architecture is responsible for PETG's characteristic transparency, lower melting point, and increased toughness. The lack of crystallinity effectively eliminates the sharp melting point seen in PET, leading to a broader softening range that is highly advantageous for thermoforming and extrusion.
Polymer family
PETG belongs to the Polyester family of thermoplastics, specifically classified as a Copolyester. Within this broad family, it sits alongside PET (Polyethylene Terephthalate), PBT (Polybutylene Terephthalate), and PCTG. Unlike PET, which is typically semi-crystalline, PETG is modified with glycol to remain permanently amorphous. It is positioned in the market as a high-performance transparent polymer that bridges the gap between Polycarbonate (more expensive, higher performance) and Acrylic (cheaper, more brittle). It is frequently grouped with other 'clear' engineering plastics and is a staple in the extrusion and thermoforming industries.
How it's made
The production of PETG begins with a polycondensation reaction between terephthalic acid (TPA) or dimethyl terephthalate (DMT) and a mixture of glycols. In PETG production, the glycol feed consists of both ethylene glycol (EG) and 1,4-cyclohexanedimethanol (CHDM). The polymerization is typically carried out in a two-stage process: ester interchange (if using DMT) or direct esterification (if using TPA), followed by vacuum polycondensation at high temperatures.
During polycondensation, the catalysts (often antimony or titanium-based) facilitate the removal of water or methanol to build up high molecular weight chains. The ratio of CHDM to EG is carefully controlled; for a material to be classified as PETG, the CHDM must be less than 50% of the total glycol content (if it's more than 50%, it becomes PCTG). Once the desired viscosity and molecular weight are achieved, the molten polymer is extruded into strands, water-cooled, and pelletized. These pellets are then often subjected to a de-volatilization process to remove any remaining residual monomers or solvents before being packaged for processors.
Advantages
- ●Superior impact resistance compared to acrylic and standard PET counterparts
- ●Excellent chemical resistance to many acids, alkalis, and oils
- ●Outstanding clarity and light transmission, often exceeding 90% in transparent grades
- ●Low processing temperatures and broad processing window for reduced energy consumption
- ●FDA and EFSA compliance for food contact and medical applications in most grades
- ●Excellent thermoforming characteristics, allowing for deep draws without blushing or whitening
- ●High ductility and toughness, maintaining performance even at low temperatures
- ●Gamma and Ethylene Oxide (EtO) sterilization compatibility for medical devices
- ●Minimal moisture absorption compared to polycarbonate, reducing the need for aggressive drying before processing
- ●Strong resistance to stress whitening during cold bending or impact events
Disadvantages
- ●Poor UV resistance; significant yellowing and embrittlement occurs during long-term outdoor exposure without UV stabilizers.
- ●Lower heat deflection temperature (HDT), typically around 70°C, limiting use in high-temperature environments.
- ●Higher notch sensitivity compared to polycarbonate, meaning sharp corners can act as failure points.
- ●Easily scratched significantly more than glass or acrylic due to its lower surface hardness (Shore R 105-115).
- ●Susceptibility to attack by certain ketones, aromatics, and chlorinated hydrocarbons.
- ●Lower structural stiffness (Flexural Modulus ~2100 MPa) compared to standard PET or Polycarbonate.
- ●Not suitable for autoclaving as it will deform at the temperatures required for steam sterilization.
When to choose it
Choose PETG when you need a material that combines high impact resistance with glass-like transparency. It is the ideal choice for heavy-duty point-of-purchase displays, machine guards, and protective glazing where acrylic would be too brittle and polycarbonate might be over-engineered or too expensive. In the medical field, PETG is the gold standard for rigid packaging and trays because it can be sterilized via gamma radiation or Ethylene Oxide without turning brittle or yellow, and its toughness ensures the sterile barrier remains intact during transport.
PETG is also the preferred choice for complex thermoforming projects involving deep draws or sharp details. Because it does not crystallize, it can be formed at lower temperatures with shorter cycle times than PET or PC, and it does not white-stress or blush during the forming process. For 3D printing, choose PETG when you need the 'easy-to-print' nature of PLA but require higher strength, chemical resistance, and better heat resistance for functional components. Use it when food safety (FDA compliance) is a requirement for containers or medical devices.
When to avoid it
PETG should be avoided in applications requiring prolonged exposure to temperatures above 65-70°C, as it will lose its structural rigidity and begin to deform. It is also unsuitable for outdoor applications where it will be exposed to direct sunlight for years, as it lacks inherent UV stability and will eventually yellow and crack. If your application requires high surface hardness or scratch resistance, such as a touch-screen interface or many years of abrasive cleaning, PETG’s relatively soft surface may be a disadvantage compared to glass or hard-coated acrylic.
From a regulatory and environmental perspective, avoid using PETG in high-volume single-use packaging that is intended for the standard municipal recycling stream. Because it is a contaminant to PET (Resin Code 1) recycling, it creates logistical challenges for waste management. Additionally, if the application requires exposure to aggressive chemicals like acetone, benzene, or methylene chloride—common in some industrial cleaning or chemical processing environments—PETG is likely to suffer from stress cracking or total dissolution.
Physical Properties
- Density
- 1.27 g/cm³
- Water Absorption (24h)
- 0.13 %
- Transparency
- Transparent
- Shrinkage
- 0.2 – 0.5 %
Mechanical Properties
- Young's Modulus
- 2.1 GPa
- Tensile Strength
- 50 MPa
- Flexural Strength
- 70 MPa
- Impact Strength (Izod)
- 100 J/m
- Elongation at Break
- 120 %
Thermal Properties
- Glass Transition Temperature
- 80 °C
- Heat Deflection Temperature
- 70 °C
- Continuous Service Temperature
- 65 °C
- CTE
- 68 × 10⁻⁶ /K
Electrical Properties
- Dielectric Constant
- 3.3
- Volume Resistivity
- 10¹⁴ Ω·cm
Chemical Resistance
- Acids
- Good
- Bases
- Fair
- Alcohols
- Good
- Oils
- Good
- UV Resistance
- Fair
Sustainability
- Recyclability
- Recyclable
- Recycling Code
- 1
- Bio-based Content
- 0 %
- Carbon Footprint
- ~2.7 kg CO₂e / kg
Process compatibility
Injection moulding
Excellent flow characteristics. Requires low-to-medium clamp pressure. Shrinkage is low (0.2-0.5%).
Extrusion molding (Sheet/Film)
Primary method for PETG. Outstanding melt strength allows for high-quality sheet and film production.
Blow moulding (EBM/ISBM)
Widely used for clear bottles. Strong melt strength prevents parison sag in extrusion blow moulding.
Thermoforming
Perhaps the best thermoforming material available. No pre-drying needed if sheet is fresh, great detail reproduction.
CNC machining
Machines well with sharp tools. Care must be taken with heat buildup to prevent gumming, but it doesn't chip as easily as acrylic.
3D printing (FDM)
The gold standard for functional FDM prints. Excellent layer adhesion and low warp. Not suitable for SLS/SLA generally.
Bonding (Solvent/Adhesive)
Responds well to solvent welding (MEK) and cyanoacrylates. Can also be ultrasonic welded.
Painting / Coating
Good adhesion for many specialized inks and paints. Surface may require corona treatment for some industrial coatings.
Manufacturing compatibility
3D Printing (FDM)Injection MoldingExtrusionThermoformingVacuum FormingLaser Cutting
Applications
Medical & Healthcare
Sterilization trays and rigid medical device packaging that must withstand gamma radiation without turning yellow or brittle.
Food & Beverage Packaging
Heavy-walled containers for oils, spirits, and personal care products where high clarity and chemical inertness are required.
Point-of-Purchase (POP) Displays
In-store shelving, product stands, and signage that require high impact resistance and complex thermoformed shapes.
Industrial Machinery Equipment
Machine guards and safety shields that offer transparent visibility with the ability to withstand high-velocity debris impacts.
Additives Manufacturing (3D Printing)
Functional prototypes and end-use mechanical jigs that require better heat resistance than PLA and easier printing than ABS.
Electronics Packaging
Anti-static electronic component carriers and clamshell packaging for consumer electronics requiring high clarity and drop protection.
Architectural Glazing
Internal partition walls and interior glazing elements that benefit from fire ratings and high impact strength in public spaces.
Orthotics & Prosthetics
Transparent check sockets for prosthetic limbs, allowing clinicians to observe pressure points on the patient's skin through the plastic.
Environmental impact
The environmental profile of PETG is mixed compared to its crystalline cousin, PET. On the positive side, it is energy-efficient to process due to its lower melting temperatures and lack of a latent heat of fusion associated with crystallinity. However, PETG presents a significant challenge in the general recycling stream. Because it is chemically similar to PET but has a much lower melting point, PETG acts as a contaminant in PET recycling. If PETG flakes enter a PET recycling melt, they soften and go 'sticky' much earlier, causing clumps in the dryer and extruder that can shut down entire processing lines.
In life cycle assessments, PETG is often preferred over PVC because it does not contain halogens like chlorine, and it does not off-gas toxic breakdown products during processing. While it is not inherently biodegradable, its durability and chemical stability make it a candidate for long-life industrial applications. Current environmental efforts for PETG focus on closed-loop industrial recycling where scrap is handled separately from post-consumer PET bottles (the #1 stream). Some manufacturers are now introducing 'recycled content' PETG grades containing up to 50% post-industrial waste to reduce the carbon footprint of virgin production.
Recycling
PETG is technically recyclable and is categorized under Resin Identification Code 7 ('Other'). While it is a polyester, it cannot be recycled with standard PET (Code 1) because the secondary glycol (CHDM) significantly lowers the melting point. In a standard PET recycling facility, PETG flakes will melt and become sticky at temperatures where PET is still solid. This causes 'clumping' on the equipment, leading to downtime and contaminated batches of rPET.
Because of this, PETG is often sorted out of municipal recycling streams and sent to landfills. However, in industrial settings, PETG scrap is highly valuable. Clean, post-industrial PETG scrap is often reground and blended back with virgin material at levels of 10-25% without significant loss in clarity or mechanical properties. For the consumer market, some specialized facilities are now using near-infrared (NIR) sorting technology to successfully separate PETG from PET to prevent stream contamination. Designers are encouraged to use PETG for durable, long-life parts rather than single-use disposables to mitigate recycling issues.
Available grades
PETG ClearPETG MedicalPETG Food GradePETG CF
Manufacturers
Equivalent materials
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Frequently asked questions
Can PETG be recycled with standard PET bottles?▾
While they are chemically similar, PETG contains CHDM to prevent crystallization. This makes PETG easier to thermoform and clearer in thick sections, but it cannot be recycled in the same stream as PET bottles (Resin Code 1).
Is PETG suitable for outdoor use?▾
In its natural state, PETG is not UV stable. It will yellow and become brittle in 6-12 months of direct sunlight. For outdoor use, UV-stabilized grades or protective coatings are required.
Is PETG food safe?▾
Yes, PETG is inherently food-safe. Most grades comply with FDA 21 CFR 177.1315 and similar EFSA guidelines, making it a standard choice for food containers and medical packaging.
How does PETG compare to Acrylic (PMMA)?▾
PETG is significantly tougher and more impact-resistant than Acrylic. However, Acrylic has better scratch resistance and superior long-term UV stability compared to PETG.
What is the maximum operating temperature for PETG parts?▾
The typical HDT of PETG is 70°C (158°F). If your application exceeds this temperature, the part will likely warp or lose structural integrity. PC or HT-PET would be better for higher temperatures.
Does PETG need to be dried before processing?▾
PETG is hygroscopic and can absorb moisture from the air. While it's less sensitive than Nylon or PC, drying at 60°C for 4-6 hours is highly recommended to prevent bubbles or 'splay' in the finished part.
Is PETG flame retardant?▾
Standard PETG is moderately flammable (UL 94 HB rating). While it doesn't burn as aggressively as some plastics, it is not inherently flame retardant. FR-rated grades are available for specific electronic applications.