Standard injection molding equipment handles copolyesters with moderate injection pressure requirements (40-100 MPa). General-purpose screws with compression ratio of 2.5:1 to 3.0:1 work well for most grades. Hot runner systems reduce waste and improve optical quality by eliminating gate vestige in multi-cavity molds. Desiccant dryers or dehumidifying hopper dryers are required to achieve moisture content below 0.02% before processing. Lower processing temperatures compared to polycarbonate reduce energy consumption and thermal stress on molding equipment.
Copolyester Overview
Copolyesters are modified polyesters known for exceptional clarity, toughness, and chemical resistance. These materials are created by adding glycol modifiers, primarily cyclohexane dimethanol (CHDM), to standard polyethylene terephthalate (PET). The resulting polymers are often called "glass polymers" because they combine glass-like transparency with the impact resistance and processability of thermoplastics. PETG (polyethylene terephthalate glycol-modified) and PCTG (polycyclohexylene dimethylene terephthalate glycol-modified) are the most common types, differentiated by their CHDM content. These materials serve critical roles in packaging, medical devices, consumer products, and point-of-purchase displays where visual appeal and durability must coexist.
Processing copolyesters involves injection molding, thermoforming, extrusion, and blow molding at temperatures ranging from 230-280°C, significantly lower than polycarbonate. The amorphous molecular structure results from CHDM modification disrupting the crystallinity of standard PET. This modification improves impact resistance, lowers processing temperatures, and enhances formability while maintaining optical clarity. The material flows smoothly in thermoforming applications, enabling deep draws and complex shapes without tearing or optical distortion. Lower melt temperatures reduce energy consumption and thermal stress compared to engineering polymers like polycarbonate or polyetherimide.
Engineers choose between PETG and PCTG based on performance requirements and cost constraints. PETG contains less than 50% CHDM and offers excellent clarity with easier processing at lower temperatures, making it suitable for cost-sensitive packaging and display applications. PCTG contains more than 50% CHDM, delivering enhanced toughness, better chemical resistance, and higher heat resistance at a 10-20% cost premium. PCTM variants incorporate additional comonomers for specialized properties like improved dimensional stability or enhanced sterilization resistance. Material selection hinges on the balance between heat exposure, chemical contact, impact requirements, and budget limitations.
Regulatory compliance positions copolyesters as viable options for food contact and medical applications. FDA 21 CFR 177.1630 approves specific grades for direct food contact, enabling use in packaging, beverage containers, and food service items. Medical-grade formulations meet USP Class VI biocompatibility standards and ISO 10993 requirements for devices contacting blood, tissue, or mucous membranes. Sterilization compatibility varies by grade, with some formulations withstanding gamma radiation (25-50 kGy), ethylene oxide (EtO), and steam autoclaving at 121°C without significant property degradation. This sterilization tolerance supports reusable medical devices requiring repeated processing cycles.
Healthcare applications leverage the unique combination of clarity and sterilizability in medical device housings, IV components, and diagnostic equipment. Packaging sectors utilize copolyesters for cosmetic bottles, premium personal care containers, and retail displays where glass-like appearance matters without glass weight or breakage risk. Consumer products benefit from impact resistance in protective equipment, sporting goods, and household storage containers. Point-of-purchase displays exploit thermoformability for creating eye-catching retail presentations with deep draws and sharp details. Electronics applications include display screens, control panel windows, and protective covers where transparency and toughness converge.
Performance Characteristics
Mechanical Properties
Tensile strength
50-60 MPa
Tensile modulus
2,000-2,400 MPa
Flexural strength
75-90 MPa
Flexural modulus
2,100-2,500 MPa
Elongation at break
100-300%
Notched Izod impact
High energy absorption, no-break performance typical
Hardness (Rockwell)
R115-120
Thermal Properties
Continuous use temperature
65-85 °C (PETG lower, PCTG higher)
Heat deflection temperature
65-85 °C at 0.46 MPa
Glass transition temperature (Tg)
75-88 °C
Melting point
None (amorphous polymer)
Processing temperature range
230-280 °C
Thermal conductivity
0.19-0.21 W/(m·K)
Flammability rating
UL94 HB (standard), V-2 to V-0 (flame-retardant grades)
Operating Environment
Water absorption
0.15-0.25% in 24h at 23°C. Lower moisture absorption than polycarbonate. Minimal dimensional changes in humid environments.
UV/weatherability rating
Fair with UV stabilizers. Unprotected grades yellow and lose mechanical properties under prolonged UV exposure. UV stabilizers required for outdoor applications.
Hydrolysis resistance
Good at room temperature. Resists hot water better than polycarbonate. Some grades withstand steam autoclaving at 121°C for medical applications.
Stress cracking sensitivity
Moderate susceptibility to environmental stress cracking with strong solvents (ketones, chlorinated hydrocarbons, aromatic solvents). Better chemical resistance than polycarbonate to alcohols and oils. Careful material selection required for applications involving solvent exposure.
Electrical Properties
Dielectric constant
(1 MHz): 2.8-3.2
Dielectric strength
15-18 kV/mm
Volume resistivity
10¹⁴-10¹⁵ ohm·cm
Dissipation factor (1 MHz)
0.010-0.015
Optical Properties
Light transmission
85-90% (clear grades, 3mm thickness)
Refractive index
1.566-1.573
Haze
<3% (clear grades)
Yellowness index
Low with UV stabilization
Physical Properties
Specific gravity
1.27-1.29
Water absorption
0.15-0.25% (24 hours at 23°C)
Shrinkage
0.5-0.7% (low and uniform due to amorphous structure)
Chemical Resistance
Excellent resistance
Alcohols, mineral oils, greases, dilute acids and bases, household chemicals and cleaners
Good resistance
Vegetable oils, fats, aliphatic hydrocarbons
Limited resistance
Strong solvents (ketones, esters, chlorinated hydrocarbons), concentrated acids and bases
Poor resistance
Aromatic hydrocarbons (toluene, xylene), strong alkalis, concentrated oxidizing agents
• Superior chemical resistance to polycarbonate for alcohols and oils; better than acrylic for impact applications
Strengths, Weaknesses, & Operating Limits
Key Strengths
- Exceptional Clarity: Glass-like transparency with 85-90% light transmission rivals polycarbonate and acrylic while maintaining superior toughness for packaging, displays, and medical devices where visual inspection matters
- Outstanding Impact Resistance: No-break performance in notched Izod testing plus high energy absorption prevents shattering in drop tests, making copolyesters ideal for protective equipment, reusable containers, and safety applications
- Superior Chemical Resistance: Resists alcohols, oils, household chemicals, and cleaning agents better than ABS or acrylic, enabling use in cosmetic packaging, healthcare environments, and consumer products exposed to various substances
- Excellent Thermoformability: Wide forming temperature window (120-160°C) with good melt strength enables deep draws, sharp detail reproduction, and complex geometries without material tearing or optical distortion
- Sterilization Compatibility: Medical grades withstand gamma radiation, ethylene oxide, and autoclave sterilization without property degradation or discoloration, meeting ISO 10993 requirements for healthcare applications
- Easy Processing: Processes at lower temperatures than polycarbonate (230-280°C vs 280-320°C), dries faster, generates less stress, reduces cycle times and energy costs in injection molding and extrusion
- FDA Food Contact Approved: Multiple grades meet FDA 21 CFR 177.1630 for food contact applications, enabling use in food packaging, beverage containers, food service items, and infant care products
Known Weaknesses
- Limited Heat Resistance: Maximum continuous use temperature 65-85°C restricts applications in hot-fill packaging, automotive under-hood components, or electronics requiring higher temperature stability compared to polycarbonate or nylon
- Solvent Sensitivity: Strong solvents like ketones, chlorinated hydrocarbons, and aromatic solvents cause stress cracking or dissolution, limiting use in industrial chemical exposure or aggressive cleaning environments
- UV Degradation: Unprotected grades yellow and lose mechanical properties under prolonged UV exposure, requiring UV stabilizers for outdoor applications unlike inherently weatherable materials such as ASA or weatherable polycarbonate
- Higher Cost Than Commodity Plastics: 2-3× more expensive than PET, PP, or PVC for similar applications, affecting material selection for high-volume, cost-sensitive consumer products or single-use packaging
- Dimensional Stability Under Load: Exhibits creep under sustained stress at elevated temperatures, requiring careful design considerations for load-bearing applications compared to engineering plastics like acetal or glass-filled nylon
Operating Limits
- Operating temperature envelope: Continuous use 65-85°C depending on grade (PCTG higher than PETG). Short-term exposure to 100-110°C acceptable. Brittle below -40°C limits cold weather outdoor applications. Elevated temperatures cause creep and dimensional changes.
- Load/time limits: Design stresses should remain below 30-35% of ultimate tensile strength for long-term static loading due to creep. Stress relaxation increases at elevated temperatures. PCTG offers better creep resistance than PETG but lower than glass-filled engineering polymers.
- Chemical/exposure limits: Avoid prolonged contact with ketones (acetone, MEK), chlorinated solvents (methylene chloride, chloroform), aromatic hydrocarbons (toluene, xylene), and concentrated acids/bases. Good resistance to alcohols, oils, and dilute chemicals at room temperature.
- Processing constraints: Dry at 65-70°C for 3-4 hours to reach <0.02% moisture. Processing temperatures 230-280°C. Lower melt viscosity than polycarbonate but requires careful gate design to prevent flow lines in optical applications. Regrind acceptable at 15-25% with proper drying.
Typical Applications
- Cosmetic packaging, premium personal care bottles, thick-walled containers for glass-like appearance
- Medical device housings, IV components, blood collection tubes, diagnostic equipment requiring transparency and sterilization
- Blister packaging, clamshells, folding cartons with windows for retail products
- Point-of-purchase displays, retail signage, protective shields for visual merchandising
- Reusable food containers, water bottles, food service items with FDA food contact compliance
- Display screens, control panel windows, protective covers for electronics
- Thermoformed packaging for consumer electronics, sporting goods, toys
- Safety equipment, protective shields, face shields requiring impact resistance and clarity
Niche Applications
- 3D printer filament (PETG, PCTG) for functional prototypes and end-use parts
- Infant care products (bottles, pacifiers) requiring BPA-free formulations like Tritan™
- Laboratory equipment, chemical storage containers, protective equipment for lab environments
- Vending machine components, coin chutes, display windows
- Machine guards for industrial equipment requiring worker visibility
- Architectural glazing for interior partitions, skylights (with UV stabilization)
- Membrane filtration housings for water treatment and pharmaceutical applications
Design, Assembly & Aesthetics
Surface finish capability
Excellent high-gloss finish achievable. Takes mold polish exceptionally well for optical surfaces. Replicates fine textures and patterns. Flow lines and weld lines visible on transparent parts without proper gate design and processing.
Sink/warpage/visible defects tendency
Minimal sink marks due to amorphous structure and low shrinkage (0.5-0.7%). Moderate warpage risk with uneven wall thickness. Gate location and cooling design critical for optical clarity. Internal stress from rapid cooling causes optical distortion.
Colorability
Excellent color range via masterbatch. Transparent, translucent, and opaque formulations available. Achieves vibrant colors and custom effects. UV stabilizers required to prevent yellowing in outdoor applications.
Color stability
Good with UV stabilization. Prolonged UV exposure without stabilizers causes yellowing. Heat-stable pigments required to prevent discoloration during processing at 230-280°C.
Optical properties
Exceptional clarity with 85-90% light transmission. Refractive index 1.566-1.573. Low haze (<3%). Internal stress causes birefringence visible under polarized light. Maintains clarity better than recycled PET.
Scratch/chemical mar resistance
Moderate scratch resistance. Good resistance to alcohols, oils, household chemicals, and cleaning agents. Superior to polycarbonate for cosmetic and personal care applications. Limited resistance to strong solvents under stress.
Marking methods
Pad printing, hot stamping, and inkjet printing good with surface treatment. Laser marking produces clear marks. Embossing and debossing produce clean features. Screen printing suitable for decorative graphics.
Coating/painting/plating suitability
Paintable with surface pretreatment (flame, plasma, corona). Clear coatings enhance scratch resistance. Metallization possible for decorative effects. Hard-coat treatments improve surface durability for glazing.
Joining methods
Ultrasonic welding produces medium-strength joints. Difficult to solvent bond to itself. Responds to solvent welding with methylene chloride or blended solvents. Adhesive bonding requires surface treatment. Mechanical fastening works well with proper boss and rib design.
Featured
Suppliers and Products
Note: As a copolyester resin supplier, Formerra provides access to Eastman's comprehensive portfolio of PETG, PCTG, and PCTM grades including UV-stabilized, flame-retardant, and FDA food contact approved formulations for packaging, medical, and consumer applications.
Neostar™
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Eastar™
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Durastar™
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Provista™
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Tritan™
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Hytrel®
View ProductsFrequently Asked Questions
Copolyesters are modified polyesters created by adding glycol modifiers like cyclohexane dimethanol (CHDM) to standard polyethylene terephthalate (PET), producing materials with exceptional clarity, toughness, and chemical resistance. The most common types are PETG (less than 50% CHDM) and PCTG (more than 50% CHDM), often called "glass polymers" for their glass-like transparency combined with plastic's impact resistance. Engineers specify copolyesters for medical devices, cosmetic packaging, point-of-purchase displays, protective equipment, and consumer products where optical clarity matters as much as durability. The material's FDA food contact approval and sterilization compatibility make it valuable in healthcare and food packaging applications where visual inspection and regulatory compliance are critical.
PETG contains less than 50% cyclohexane dimethanol (CHDM) modification while PCTG contains more than 50% CHDM, creating measurable differences in performance and cost. PETG offers excellent clarity and easier processing at lower temperatures (230-260°C) with slightly lower heat resistance (continuous use to 65°C), making it ideal for cost-sensitive applications like retail packaging, single-use medical devices, and general thermoforming. PCTG provides enhanced toughness, better chemical resistance, and higher heat resistance (continuous use to 85°C) at 10-20% premium cost, specified for durable medical equipment requiring repeated sterilization, premium cosmetic bottles exposed to oils and fragrances, and applications needing better dimensional stability under load. Both maintain similar optical clarity (85-90% light transmission), but PCTG's superior properties justify its higher cost when thermal or chemical demands exceed PETG's capabilities.
Copolyesters cost 30-40% less than polycarbonate (PC) while offering superior chemical resistance to alcohols, oils, and household cleaners that cause PC stress cracking, making them preferred for cosmetic packaging and applications involving chemical exposure. PC provides significantly better heat resistance (continuous use 115-130°C vs 65-85°C for copolyester) and higher impact strength, specified for automotive components, electrical housings, and applications requiring elevated temperature performance. Both materials offer excellent clarity (85-90% light transmission), but copolyesters process at lower temperatures (230-280°C vs 280-320°C for PC), reducing energy costs, cycle times, and thermal stress on inserts in overmolding operations. Material selection depends on performance requirements: choose copolyester when chemical resistance, thermoformability, and lower cost matter more than heat resistance; select PC when temperature capability and maximum impact strength justify higher material cost and processing temperatures.
Injection molding processes copolyesters at 230-280°C barrel temperature with 10-40°C mold temperature, requiring 3-4 hour drying at 65-70°C to reach sub-0.02% moisture content for optical clarity. Thermoforming heats extruded sheet to 120-160°C forming temperature, enabling deep draws and complex geometries without material tearing or optical distortion in packaging and display applications. Extrusion produces sheet and profiles at 230-270°C die temperature with careful cooling control to maintain optical properties and dimensional stability. Blow molding creates bottles and containers using stretch blow molding equipment with precise temperature control for wall thickness uniformity. All processes benefit from copolyester's lower processing temperatures compared to polycarbonate, reducing energy costs and thermal stress while achieving excellent surface finish and optical quality with proper parameter control.
Copolyester carries recycling code 1 (PET family) or 7 (other plastics) depending on jurisdiction and is recyclable through mechanical recycling processes. Post-industrial scrap from injection molding and thermoforming can be reground and reprocessed with virgin material at typical ratios of 15-25% regrind. Recycled copolyester maintains acceptable properties for many applications though repeated processing cycles cause slight yellowing and minor property degradation. Post-consumer copolyester recycling is limited by collection infrastructure and contamination with PET and other plastics. Separation from PET recycling streams is challenging due to similar density and appearance. Some manufacturers offer recycled-content copolyester grades and bio-based alternatives like Eastman Tritan™ Renew using molecular recycling technology. Material selection should consider end-of-life requirements and regional recycling capabilities.
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ASTM D4802: Standard Specification for Poly(Ethylene Terephthalate) Materials for Molding and Extrusion
ISO 10993: Biological Evaluation of Medical Devices
FDA 21 CFR 177.1630: Polyethylene terephthalate polymers
USP Class VI Biological Reactivity Tests for Plastics
Eastman Copolyester Product Guide. Eastman Chemical Company. 2025.