Polyethylene terephthalate (or poly(ethylene terephthalate), PET, PETE, or the obsolete PETP or PET-P) is the most common thermoplastic polymer resin of the polyester family and is used in fibres for clothing, containers for liquids and foods, and thermoformed parts for manufacturing, and in combination with glass fibre for engineering resins.
In 2025, annual global production of PET was 31 million tons with 2031 projections showing over 40 million tons. In the context of textile applications, PET is referred to by its common name, polyester, whereas the acronym PET is generally used in relation to packaging. PET used in non-fiber applications (i.e. for packaging) makes up about 6% of world polymer production by mass. Including the >60% fraction of polyethylene terephthalate produced for use as polyester fibers, PET is the fourth-most-produced polymer after polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC).
PET consists of repeating (C10H8O4) units. It is commonly recycled, and has the digit 1 (♳) as its resin identification code (RIC). The National Association for PET Container Resources (NAPCOR) defines PET as: "Polyethylene terephthalate items referenced are derived from terephthalic acid (or dimethyl terephthalate) and mono ethylene glycol, wherein the sum of terephthalic acid (or dimethyl terephthalate) and mono ethylene glycol reacted constitutes at least 90 percent of the mass of monomer reacted to form the polymer, and must exhibit a melting peak temperature between 225 °C and 255 °C, as identified during the second thermal scan in procedure 10.1 in ASTM D3418, when heating the sample at a rate of 10 °C/minute."
Depending on its processing and thermal history, polyethylene terephthalate may exist both as an amorphous (transparent) and as a semi-crystalline polymer. The semicrystalline material might appear transparent (particle size less than 500 nm) or opaque and white (particle size up to a few micrometers) depending on its crystal structure and particle size.
One process for making PET uses bis(2-hydroxyethyl) terephthalate, which can be synthesized by the esterification reaction between terephthalic acid and ethylene glycol with water as a byproduct (this is also known as a condensation reaction), or by transesterification reaction between ethylene glycol and dimethyl terephthalate (DMT) with methanol as a byproduct. It can also be obtained by recycling of PET. Polymerization is through a polycondensation reaction of the monomers (done immediately after esterification/transesterification) with water as the byproduct.
Young's modulus, E 2800–3100 MPa Tensile strength, σt 55–75 MPa Elastic limit 50–150% Notch test 3.6 kJ/m2 Glass transition temperature, Tg 67–81 °C Vicat B 82 °C Linear expansion coefficient, α Water absorption (ASTM) 0.16 Source
Uses
Textiles Polyester fibres are widely used in the textile industry. The invention of the polyester fibre is attributed to J. R. Whinfield. It was first commercialized in the 1940s by ICI, under the brand 'Terylene'.The name Terylene was formed by inversion of (polyeth)ylene ter(ephthalate) and dates to the 1940s. Oxford Dictionary. Terylene was first registered as a UK trademark in April 1946. UK Intellectual Property Office Subsequently E. I. DuPont launched the brand 'Dacron'. As of 2022, there are many brands around the world, mostly Asian.
Polyester fibres are used in fashion apparel often blended with cotton, as heat insulation layers in thermal wear, sportswear and workwear and automotive upholstery.
Rigid packaging Plastic bottles made from PET are widely used for soft drinks, both still and sparkling. For beverages that are degraded by oxygen, such as beer, a multilayer structure is used. PET sandwiches an additional polyvinyl alcohol (PVOH) or polyamide (PA) layer to further reduce its oxygen permeability.
Non-oriented PET sheet can be thermoformed to make packaging trays and blister packs. Both amorphous PET and biaxially oriented PET (BoPET) are transparent to the naked eye. Dyes can easily be formulated into PET sheet.
PET is permeable to oxygen and carbon dioxide and this imposes shelf life limitations of contents packaged in PET.
In the early 2000s, the global PET packaging market grew at a compound annual growth rate of 9% to €17 billion in 2006.
Flexible packaging Biaxially oriented PET (BoPET) film can be aluminized by evaporating a thin film of metal onto it to reduce its permeability, and to make it reflective and opaque (MPET). These properties are useful in many applications, such as increasing shelf life of products, including flexible food packaging and thermal insulation (such as space blankets).
Photovoltaic modules BoPET is used in the backsheet of photovoltaic modules. Most backsheets consist of a layer of BOPET laminated to a fluoropolymer or a layer of UV stabilized BOPET. PET is also used as a substrate in thin film solar cells.
Thermoplastic resins PET can be compounded with glass fibre and crystallization accelerators, to make thermoplastic resins. These can be injection moulded into parts such as housings, covers, electrical appliance components and elements of ignition systems.
Other applications A waterproofing barrier in undersea cables. As a film base. As a fibre, spliced into bell rope tops to help prevent wear on the ropes as they pass through the ceiling. Since late 2014 as liner material in type IV composite high pressure gas cylinders. PET works as a much better barrier to oxygen than earlier used low density polyethylene (LDPE). As a 3D printing filament, as well as in the 3D printing plastic polyethylene terephthalate glycol (PETG). In 3D printing PETG has become a popular material - used for high-end applications like surgical fracture tables. And in the automotive and aeronautical sectors, among other industrial applications. The surface properties can be modified to make PETG self-cleaning for applications like the fabrication of traffic signs for the manufacture of LED spotlights. As one of three layers for the creation of glitter; acting as a plastic core coated with aluminum and topped with plastic to create a light reflecting surface, although as of 2021 many glitter manufacturing companies have begun to phase out the use of PET after calls from organizers of festivals to create bio-friendly glitter alternatives. Film for tape applications, such as the carrier for magnetic tape or backing for pressure-sensitive adhesive tapes. Digitalization has caused the virtual disappearance of the magnetic audio and videotape application. Water-resistant paper.
History PET was patented in 1941 by John Rex Whinfield, James Tennant Dickson and their employer the Calico Printers' Association of Manchester, England. E. I. DuPont de Nemours in Delaware, United States, first produced Dacron (PET fiber) in 1950 and used the trademark Mylar (boPET film) in June 1951 and received registration of it in 1952.Whinfield, John Rex and Dickson, James Tennant (1941) "Improvements Relating to the Manufacture of Highly Polymeric Substances", UK Patent 578,079; "Polymeric Linear Terephthalic Esters", Publication date: 22 March 1949; Filing date: 24 September 1945; Priority date: 29 July 1941 It is still the best-known name used for polyester film. The current owner of the trademark is DuPont Teijin Films.TEIJIN: Trademarks "Mylar and Melinex are the registered trademarks or trademarks of Dupont Teijin Films U.S. Limited Partnership and have been licensed to Teijin DuPont Films Japan Limited"
In the Soviet Union, PET was independently developed in the laboratories of the Institute of High-Molecular Compounds of the USSR Academy of Sciences in 1949, and its Russian name "Lavsan" is an acronym thereof (лаборатории Института высокомолекулярных соединений Академии наук СССР).
The PET bottle was invented in 1973 by Nathaniel Wyeth and patented by DuPont.
Physical properties
PET in its most stable state is a colorless, semi-crystalline resin. However it is intrinsically slow to crystallize compared to other semicrystalline polymers. Depending on processing conditions it can be formed into either non-crystalline (amorphous) or crystalline articles. Its amenability to drawing in manufacturing makes PET useful in fibre and film applications. It is strong and impact-resistant. PET is hygroscopic.
Transparent products can be produced by rapidly cooling molten polymer below the glass transition temperature (Tg) to form a non-crystalline amorphous solid. Amorphous PET forms by rapidly cooling the melt. This glassy state tends to crystallize upon heating the material above Tg, a process known as cold crystallization. Amorphous PET also crystallizes and becomes opaque when exposed to some solvents, such as chloroform or toluene.NPCS Board of Consultants & Engineers (2014) Chapter 6, p. 56 in Disposable Products Manufacturing Handbook, NIIR Project Consultancy Services, Delhi,
A more crystalline product can be produced by cooling the molten polymer slowly. Rather than forming one large single crystal, this material has a number of spherulites (crystallized areas) each containing many small crystallites (grains). Light tends to scatter as it crosses the boundaries between crystallites and the amorphous regions between them, causing the resulting solid to be translucent. Orientation also renders polymers more transparent. This is why BOPET film and bottles are both crystalline, to a degree, and transparent.
Flavor absorption PET has an affinity for hydrophobic flavors, and drinks sometimes need to be formulated with a higher flavor dosage, compared to those going into glass, to offset the flavor taken up by the container. When returned for reuse, as in some EU countries, PET's propensity to absorb flavors makes it necessary to conduct a "sniffer test" on some returned bottles to avoid cross-contamination of flavors.
Intrinsic viscosity Different applications of PET require different degrees of polymerization, which can be obtained by modifying the process conditions. The molecular weight of PET is measured by solution viscosity. Viscosity is highly dependent on molecular parameters such as chain length and molecular weight. Due to the structural complexity of branched polymers, viscosity-based determination of molecular weight is best used with linear polymers. With dilute solutions, an empirical relationship can be derived between the viscosity and the hydrodynamic volume and molecular weight distribution. The preferred method to measure this viscosity is the intrinsic viscosity (IV) of the polymer.Thiele, Ulrich K. (2007) Polyester Bottle Resins, Production, Processing, Properties and Recycling, Heidelberg, Germany, pp. 85 ff, Intrinsic viscosity is a dimensionless measurement found by extrapolating the relative viscosity (measured in (dℓ/g)) to zero concentration. Shown below are the IV ranges for common applications:Gupta, V.B. and Bashir, Z. (2002) Chapter 7, p. 320 in Fakirov, Stoyko (ed.) Handbook of Thermoplastic Polyesters, Wiley-VCH, Weinheim, . +ApplicationIVTextile fibers0.40–0.70Technical fibers (e.g. tire cord)0.72–0.98Biaxially oriented PET film (BOPET)0.60–0.70Sheet grade film for thermoforming0.70–1.00General purpose bottles0.70–0.78Carbonated drink bottles0.78–0.85Monofilaments and engineering plastics1.00–2.00
Copolymers
PET is often copolymerized with other diols or diacids to optimize the properties for particular applications.
PETG