Properties of Polyethylene Terephthalate Polyester (PET, PETP)

Updated by Reginald Davey 11/07/23

Polyethylene terephthalate polyester (PET or PETE)is the most common thermoplastic polyester. It is commonly referred to as “polyester.” Polybutylene (PBT,) another thermoplastic polymer, is chemically similar to PET and is also known as polyester.

Polyethylene Terephthalate Polyester, properties of polyethylene terephthalate

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PBT is the most common resin system used in GRP. In a polyester system, the main difference between PBT and polyethylene terephthalate is that it incorporates chemically unsaturated polyesters and are “free radical polymerized” into a thermoset.

General Properties of Polyester Terephthalate

There are several properties of polyester terephthalate that inform its industrial and commercial uses. PETE is a hard, stiff, strong, and dimensionally stable material that has very low water absorption behavior. It also has good gas barrier properties and good chemical resistance except to alkalis (which hydrolyse it).

PETE varies from an amorphous to relatively higher crystalline state. Its appearance can be colorless and transparent, or in thicker sections, off-whire and opaque.

Polyethylene Terephthalate Films

PETE is widely commercially available in the form of biaxially oriented and thermally stabilized films, usually referred to by their main brand names Mylar, Melinex, or Hostaphan.

Strictly speaking, these names should be used only for this type of film whose properties are different from, and in several respects superior to, those of “ordinary” polyethylene terephthalate (PET) film.


PETE films are used for capacitors, graphics, film bases, recording tapes, etc. It is also used as fiber in a very wide range of textile and industrial uses (Dacron®, Trevira®, Terylene®).

Uses include both rigid and flexible packaging, textiles, electrical components, bottles, thermoplastic resin, undersea cables, high-pressure gas cylinders, and photovoltaic modules.

Key Properties of Polyethylene Terephthalate

The key properties of Polyethylene Terephthalate Polyester are tabulated below.

Table 1. Key properties

Chemical Resistance
Acids – concentrated Good
Acids – dilute Good
Alcohols Good
Alkalis Poor
Aromatic hydrocarbons Fair
Greases and Oils Good
Halogens Good
Ketones Good
Electrical Properties
Dielectric constant @ 1 MHz 3.0
Dielectric strength ( ) 17
Dissipation factor @ 1 kHz 0.002
Surface resistivity ( Ohm/sq ) 1013
Volume resistivity ( ) >1014
Mechanical Properties
Coefficient of friction 0.2 - 0.4
Hardness – Rockwell M94-101
Izod impact strength ( J.m-1 ) 13 - 35
Poisson’s ratio 0.37-0.44 (oriented)
Tensile modulus ( GPa ) 2 - 4
Tensile strength ( MPa ) 80, for biax film 190 - 260
Physical Properties
Density ( ) 1.3 - 1.4
Flammability Self Extinguishing
Limiting oxygen index ( % ) 21
Refractive index 1.58 - 1.64
Resistance to Ultra-violet Good
Water absorption - equilibrium ( % ) <0.7
Water absorption - over 24 hours ( % ) 0.1
Thermal Properties
Coefficient of thermal expansion ( x10-6 K-1 ) 20 - 80
Heat-deflection temperature - 0.45 MPa ( °C ) 115
Heat-deflection temperature - 1.8 MPa ( °C ) 80
Lower working temperature ( °C ) -40 to -60
Specific heat ( ) 1200 - 1350
Thermal conductivity ( W.m-1.K-1 ) 0.15 - 0.4 @ 23
Upper working temperature ( °C ) 115 - 170
Properties Polyethylene Terephthalate Film
Property   Value
Dielectric Strength @ 25 µm thick 300
Dissipation Factor @ 1 MHz   0.016
Elongation at Break % 60 - 165
Initial Tear Strength g.µm-1 18 - 54
Permeability to Carbon Dioxide
@ 25 °C
x10-13 0.07 - 0.11
Permeability to Hydrogen @ 25 °C x10-13 0.45
Permeability to Nitrogen @ 25 °C x10-13 0.0034 - 0.0038
Permeability to Oxygen @ 25 °C X10-13 0.015 - 0.04
Permeability to Water @ 25 °C X10-13 100 - 115
Specific Heat 1.3
Thermal Conductivity @ 23 °C W.m-1.K-1 0.13 - 0.15
Properties Polyethylene Terephthalate Fibre
Property   Value
Material   Medium High tenacity
Specific Modulus cN/tex   700 - 800
Specific Tenacity cN/tex 36 70 - 80
Density 1.39 1.39
Extension to break % 36 13 - 16
Modulus GPa   9 - 11
Shrinkage @ 100 °C % 4 1.5 - 6
Tenacity GPa 0.5 0.9 - 1.1


In Summary

PETE (otherwise known as polyester) is an eminently useful thermoplastic polymer for many applications. This is down to the beneficial physical, chemical, electrical, and thermal properties of polyester terephthalate.

Whilst it possesses several advantages, there are some main disadvantages to using PETE. These include lower heat resistance, potential oxidation of resins, and its lack of biodegradability. However, it continues to be one of the most widely used polymers in the 21st century.

Further Reading and More Information (website) PET – Polyethylene Terephthalate [online] Available at: (website) PET – Density – Strength – Melting Point – Thermal Conductivity [online] Available at:

Team Xometry (2022) Polyethylene Terephthalate: Uses, Advantages, and Disadvantages [online] Available at:

Encylopedia Britannica (2023) Polyethylene terephthalate [online] Available at:


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  1. rajasundar amirthalingam rajasundar amirthalingam India says:

    UV Resistance - any scale is there?

  2. Klausberg Sampaio Klausberg Sampaio Brazil says:

    What can I use glue to paste PETg

  3. ganga dharan ganga dharan India says:

    Where is the chemical properties

  4. Amadi Juliet Amadi Juliet Nigeria says:

    PETP as same as polyester films and it's uses.

  5. Sunil Gavaskar Sunil Gavaskar India says:

    How to read thermal conductivity. Is this low conductivity compare to natural material jute ?

  6. Michael WISTBACKA Michael WISTBACKA Philippines says:

    G PEt what is G for and where to find

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