View source for Mylar

{{Short description|Polyester film}}
[[Image:Myla32rp.jpg|thumb|right|[[Metallised film|Metallized boPET]] film, 32 layers of ~14&nbsp;μm thickness each]]

'''BoPET''' ('''biaxially oriented polyethylene terephthalate''') is a [[polyester]] film made from stretched [[polyethylene terephthalate]] (PET) and is used for its high [[tensile strength]],<ref name=":0" /> [[chemical stability]],<ref name=":0" /> [[dimensional stability (fabric)|dimensional stability]],<ref name=":1" /> [[Transparency (optics)|transparency]]<ref name=":0" /> [[reflectivity]], and [[electrical insulation]].<ref name=":0" />  When [[Metallised film|metallized]], it has gas and moisture barrier properties.<ref name=":2" /> The film is "biaxially oriented", which means that the polymer chains are oriented parallel to the plane of the film, and therefore oriented over two axes.<ref name=":2">{{Cite book |last=Drobny |first=Jiri George |url=https://books.google.com/books?id=cIDRAgAAQBAJ |title=Handbook of Thermoplastic Elastomers |date=2014-05-30 |publisher=Elsevier |isbn=978-0-323-22168-9 |language=en}}</ref> A variety of companies manufacture boPET and other polyester films under different [[brand name]]s. In the UK and US, the best-known trade names are '''Mylar''', '''Melinex''', '''Lumirror''' and '''Hostaphan'''.<ref>{{cite book |url= https://books.google.com/books?id=BXpwAgAAQBAJ&pg=PA48 |page=48 |title= Biaxial Stretching of Film: Principles And Applications |author= Mark T. DeMeuse |publisher= Elsevier |year= 2011|isbn=9780857092953 }}</ref> It was the first biaxially oriented polymer to be manufactured on a mass commercial scale.<ref>{{Cite book |last1=Jenkins |first1=Wilmer A. |url=https://books.google.com/books?id=wpkaIV_nxWMC |title=Plastic Films: echnology and Packaging Applications |last2=Osborn |first2=Kenton R. |date=1992-09-25 |publisher=CRC Press |isbn=978-0-87762-843-9 |language=en}}</ref>

== History ==
BoPET film was developed in the mid-1950s,<ref name=Izard>Izard, Emmette Farr, [https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/2534028 "Production of polyethylene terephthalate"], U.S. patent no. 2,534,028 (filed: 1948 May 13; issued:  1950 December 12).</ref><ref>Adams, John Francis Edward; Gerber, Kenneth George; Holmes-Walker, William Anthony, [http://pdfpiw.uspto.gov/.piw?Docid=03177277&homeurl=http%3A%2F%2Fpatft.uspto.gov%2Fnetacgi%2Fnph-Parser%3FSect2%3DPTO1%2526Sect2%3DHITOFF%2526p%3D1%2526u%3D%2Fnetahtml%2FPTO%2Fsearch-bool.html%2526r%3D1%2526f%3DG%2526l%3D50%2526d%3DPALL%2526S1%3D3177277.PN.%2526OS%3DPN%2F3177277%2526RS%3DPN%2F3177277&PageNum=&Rtype=&SectionNum=&idkey=NONE&Input=View+first+page "Process for the production of biaxially oriented polyethylene terephthalate film"], U.S. patent no. 3,177,277 (filed: 1957 May 10; issued: 1965 April 6).</ref> originally by [[DuPont (1802–2017)|DuPont]],<ref name=Izard/> [[Imperial Chemical Industries]] (ICI), and [[Hoechst AG|Hoechst]]. [[Buckminster Fuller]] used Mylar in 1953 as a skin for a [[geodesic dome]], which he built with students at the [[University of Oregon]].<ref>{{citation | title=Fuller Directs Installation Of Dymaxion-Type Dome| publisher=[[Oregon Daily Emerald]]|date=April 10, 1953| url=https://oregonnews.uoregon.edu/lccn/2004260239/1953-04-10/ed-1/seq-7.pdf }}</ref> [[Eastman Kodak]] used Mylar in 1955 as a support for photographic film and called it "ESTAR Base".<ref name="KodakESTAR">{{cite web |title=Kodak HCF Film/ESTAR Base |url=https://www.kodak.com/uploadedFiles/Corporate/Industrial_Materials_Group/E4058_HCFFilm.pdf |website=www.kodak.com |publisher=[[Eastman Kodak Company]] |access-date=2018-08-24 |date=April 2015}}</ref> The very thin and tough film allowed {{convert|6000|ft|adj=on}} reels to be exposed on long-range [[Lockheed U-2|U-2]] reconnaissance flights.<ref>''Eyes in the Sky'', Dino A. Brugioni 2010, Naval Institute Press, {{ISBN|978 1 59114 082 5}}, pp. 102, 115.</ref> [[NASA]] launched [[Project Echo#Echo 2|Echo II]] in 1964, a {{convert|40|m|ft|0|adj=on}} diameter balloon constructed from a {{convert|9|μm|in|adj=on}} thick boPET film sandwiched between two layers of {{convert|4.5|μm|in|adj=on}} thick aluminium foil bonded together.<ref>Staugaitis, C. & Kobren, L. (1966) "Mechanical And Physical Properties of the Echo II Metal-Polymer Laminate (NASA TN D-3409)", NASA Goddard Space Flight Center.</ref>

== Manufacture and properties ==
{{more citations needed section|date=January 2023}}
[[Image:Polyethylene terephthalate.svg|thumb|upright=1.35|Chemical structure of polyethylene terephthalate]]

The manufacturing process begins with a film of molten [[polyethylene terephthalate]] (PET) being [[Plastics extrusion|extruded]] onto a chill roll, which quenches it into the amorphous state. It is then biaxially oriented by [[Drawing (manufacturing)|drawing]]. The most common way of doing this is the sequential process, in which the film is first drawn in the machine direction using heated rollers and subsequently drawn in the transverse direction, i.e., [[orthogonality|orthogonally]] to the direction of travel, in a heated oven. It is also possible to draw the film in both directions simultaneously, although the equipment required for this is somewhat more elaborate. Draw ratios are typically around 3 to 4 in each direction.

Once the drawing is completed, the film is "[[heat set]]" and [[crystal]]lized under tension in the oven at temperatures typically above {{convert|200|C}}.<ref name=":3">{{Cite book |last=DeMeuse |first=Mark T. |url=https://books.google.com/books?id=BXpwAgAAQBAJ |title=Biaxial Stretching of Film: Principles and Applications |date=2011-07-18 |publisher=Elsevier |isbn=978-0-85709-295-3 |language=en}}</ref> The heat setting step prevents the film from shrinking back to its original unstretched shape and locks in the molecular orientation in the film plane.{{Citation needed|date=June 2024}} The orientation of the polymer chains is responsible for the high strength and stiffness of biaxially oriented PET film, which has a typical [[Young's modulus]] of about  {{cvt|4|GPa|e6psi}}. Another important consequence of the molecular orientation is that it induces the formation of many crystal nuclei. The crystallites that grow rapidly reach the boundary of the neighboring crystallite and remain smaller than the wavelength of visible light. As a result, biaxially oriented PET film has excellent clarity, despite its [[semicrystalline]] structure.

If it were produced without any additives, the surface of the film would be so smooth that layers would adhere strongly to one another when the film is wound up, similar to the sticking of clean glass plates when stacked. To make handling possible, microscopic inert inorganic particles, such as [[silicon dioxide]], are usually embedded in the PET to roughen the surface of the film.<ref>{{cite web |last1=Thiel |first1=Ulrich |title=Polyester Additives |url=https://www.polyester-technology.com/fileadmin/media/literature/70-Thiele_POLYESTER-ADDITIVES-LONGVERSION-2007.pdf.pdf |website=Dr. Thiele Polyester Technology |access-date=4 January 2019}}</ref>

Biaxially oriented PET film can be [[Metallised film|metallized]] by [[vapor deposition]] of a [[Thin-film deposition|thin film]]  of [[evaporation|evaporated]] [[aluminium]], [[gold]], or other metal onto it. The result is much less permeable to gases (important in [[Modified atmosphere|food packaging]]) and reflects up to 99% of light{{citation needed|date=October 2021}}, including much of the [[infrared]] spectrum. For some applications like food packaging, the aluminized boPET film can be laminated with a layer of [[polyethylene]], which provides [[Heat sealer#Heat sealing process|sealability]] and improves [[puncture resistance]]. The polyethylene side of such a laminate appears dull and the boPET side shiny.{{Citation needed|date=June 2024}} Other coatings, such as conductive [[indium tin oxide]] (ITO), can be applied to boPET film by [[sputter deposition]].{{Citation needed|date=June 2024}}

== Applications ==
{{more citations needed section|date=January 2023}}
Uses for boPET polyester films include, but are not limited to:

=== Flexible packaging and food contact ===
[[File:Seafood Packaging (96-132-17a).jpeg|thumb|right|NASA's Technology Transfer Office at Stennis Space Center worked with a New Orleans seafood packaging company to develop a container to improve the shipping longevity of seafood, primarily frozen and fresh fish, while preserving the taste. A NASA engineer developed metalized heat resistant polybags with thermal foam liners using an enhanced version of the metalized mylar commonly known as "space blanket material," which was produced during the Apollo era.]]
* Laminates containing metallized boPET foil (in technical language called printin{{typo help inline|reason=similar to printing|date=September 2022}} or laminate web substrate) protect food against oxidation and aroma loss, achieving long [[shelf life]]. Examples are coffee "foil" packaging and pouches for convenience foods.
*[[Pop-Tarts]] toaster pastries are sold in pairs wrapped in silver boPET. They were previously{{when |date=September 2025}} wrapped in foil.
* White boPET web substrate is used as lidding for dairy goods such as [[yogurt]].
* Clear boPET web substrate is used as lidding for fresh or frozen ready meals. Due to its excellent heat resistance, it can remain on the package during microwave or oven heating.
* boPET is used as a material for roasting bags
* [[Metallised film]] is related to boPET
* Laminated sheet metal (aluminium or steel) used in the manufacture of cans ([[bisphenol A]]-free alternative to lacquers) has some relationship with boPET

===Covering over paper===
* A clear overlay on a [[map]], on which notations, additional [[data]], or copied data, can be drawn without damaging the map
* Metallized boPET is used as a mirror-like decorative surface on some book covers, T-shirts, and other flexible cloths.
* Protective covering over buttons/pins/[[badge]]s
* The glossy top layer of a [[Polaroid SX-70]] photographic print
* As a backing for very fine [[sandpaper]]
* boPET film is used in bagging [[comic books]], in order to best protect them during storage from environmental conditions (moisture, heat, and cold) that would otherwise cause paper to slowly deteriorate over time. This material is used for [[Archival science|archival quality]] storage of documents by the [[Library of Congress]] (Mylar type D, ICI Melinex 516 or equivalent)<ref>{{cite web|title=Specifications for Polyester: Poly(ethylene-terephthalate)|url=http://lcweb.loc.gov/preserv/supply/specs/500-500.html|work=Preservation|publisher=Library of Congress|url-status=dead|archive-url=https://web.archive.org/web/20040623151837/http://lcweb.loc.gov/preserv/supply/specs/500-500.html|archive-date=June 23, 2004}}</ref><ref>{{cite web|url=http://www.jampaper.com/blog/what-is-mylar-paper/|title=What is Mylar Paper - More Than Just Decoration|work=Jampaper.com|date=23 October 2013|access-date=2015-07-02}}</ref> and several major library comic book research collections, including the Comic Art Collection at [[Michigan State University]].<ref name=":0">{{cite journal |last=Scott |first=Randall W. |title=A Practicing Comic-Book Librarian Surveys His Collection and Craft |journal=Serials Review |volume=24 |issue=1 |year=1998 |pages=49&ndash;56 |doi=10.1080/00987913.1998.10764429 }}</ref>  While boPET is widely (and effectively) used in this archival sense, it is not immune to the effects of fire and heat and could potentially melt, depending on the intensity of the heat source, causing further damage to the encased item.<ref>{{cite web|url=http://www.myacpl.org/node/618|title=Albany library's entire collection exposed to smoke|work=Athens Messenger|via=Athens County Public Libraries|author=Kristen Heinichen|date=June 17, 2008|access-date=2015-07-02|archive-url=https://web.archive.org/web/20150703083704/http://www.myacpl.org/node/618 |archive-date=2015-07-03 |url-status=dead}}</ref>
* Similarly, [[collectible card game|trading card]] decks (such as ''[[Pokémon Trading Card Game|Pokémon]]'', ''[[Magic: The Gathering]]'', and ''[[Yu-Gi-Oh! Trading Card Game|Yu-Gi-Oh!]]'') are packaged in pouches or sleeves made of metallized boPET. It can also be used to make the holographic artwork featured on some cards, typically known as "holos", "foils", "shinies", or "holofoils".
*For protecting the spine of important documents, such as [[medical records]].

===Insulating material===
{{unreferenced section|date=July 2025}}
* An [[Electrical insulation|electrical insulating]] material
* [[Thermal insulation|Insulation]] for houses and tents, reflecting thermal radiation
* Five layers of metallized boPET film in NASA's [[spacesuit]]s make them [[radiation]] resistant and help regulate temperature.
* Metallized boPET film [[Space blanket|emergency blankets]] conserve a [[shock (circulatory)|shock]] victim's body heat.
* As a thin strip to form an airtight seal between the control surfaces and adjacent structure of aircraft, especially [[Glider aircraft|glider]]s.
* Light insulation for indoor gardening.
* [[Fire proximity suit|Aluminized proximity suits]] used by fire fighters for protection from the high amount of heat release from fuel fires.
* Used in sock and glove liners to lock in warmth
* Gasketing material in [[fuel cell]]s and related devices

===Solar, marine, and aviation===
* Metallized boPET is intended to be used for [[solar sail]]s as an alternative [[spacecraft propulsion|means of propulsion]] for [[spacecraft]] such as [[Cosmos 1|Cosmos&nbsp;1]]{{cn|date=July 2025}}
* Translucent Mylar film, as wide as {{convert|4|ft}} and up to {{convert|12|ft}} in length, found widespread use as a non-dimensional engineering drawing media in the aerospace industry due to its dimensional stability (also see Printing Media section below). This allows production and engineering staff to lay manufactured parts directly over or under the drawing film in order to verify the fidelity of part profiles, hole locations and other part features.<ref name=":1">{{cite web|url=https://www.cadcam.org/blog/convert-mylar-aerospace-drawings-3d-cad/ |title=How to Convert Mylar Aerospace Drawings to 3D CAD|date=31 January 2018|publisher=CAD / CAM Services}}</ref>
* Metallized boPET [[Sun|solar]] curtains, to reflect sunlight and heat away from windows.{{cn|date=July 2025}}
* Aluminized, as an inexpensive [[solar eclipse]] viewer.{{cn|date=July 2025}}
* High performance [[sail]]s for [[sailboat]]s, [[Hang gliding|hang gliders]], [[Paragliding|paragliders]] and [[Kitesurfing|kites]]{{cn|date=July 2025}}
* As the back face of the PV modules in solar panels.{{cn|date=July 2025}}
* To bridge control surface gaps on [[sailplane]]s (gliders), reducing [[profile drag]].{{cn|date=July 2025}}

===Science===
{{unreferenced section|date=July 2025}}
* Amateur and professional visual and telescopic [[solar filter]]s. BoPET films are often annealed to a glass element in telescopic applications for stability.
* Films in annular ring mounts on gas-tight cells, which will readily deform into spherical mirrors. [[Photomultiplier]] [[cosmic-ray]] observatories often make use of these mirrors.
* As a light diaphragm material separating gases in hypersonic shock and expansion tube facilities.
* As a [[beamsplitter]] in [[Fourier transform infrared spectroscopy]], typically with [[laser]] applications.
* Coating around [[Hematocrit|hematocrit tubes]].
* Insulating material for a cryocooler radiation shield.
* As a window material to confine gas in detectors and targets in [[nuclear physics]].
* In [[CT Scanner|CT scanners]] it acts as a physical barrier between the X-ray tube, detector ring and the patient allowing negligible attenuation of the X-ray beam when active.
* Spacecraft are insulated with a metallized BoPET film.

===Electronic and acoustic===
{{unreferenced section|date=July 2025}}
* Carrier for flexible printed circuits.
* BoPET film is often used as the [[Diaphragm (acoustics)|diaphragm]] material in [[headphones]], [[electrostatic loudspeaker]]s and [[microphone]]s.
* BoPET film has been used in the production of [[banjo]]s and [[drumhead]]s since 1958 due to its durability and acoustical properties when stretched over the bearing edge of the drum. They are made in single- and double-ply versions, with each ply being {{convert|2|-|10|mil}} in thickness, with a [[Transparency and translucency|transparent]] or [[Opacity (optics)|opaque]] surface, originally used by the company [[D'Addario (manufacturer)|Evans]].
* BoPET film is used as the substrate in practically all [[magnetic tape|magnetic recording tape]]s and [[floppy disk]]s.
* Metallized boPET film, along with other plastic films, is used as a [[dielectric]] in foil [[capacitor]]s.
* Clear boPET bags are used as [[packaging]] for audio media such as [[compact disc]]s and [[vinyl record]]s.
* Clear and white boPET films are used as core layers and overlays in [[Smart Card|smart card]]s.

===Printing media===
{{unreferenced section|date=July 2025}}
* Before the widespread adoption of [[Computer-aided design|computer aided design]] (CAD), [[engineering drawings]] or [[architectural drawing]]s were plotted onto sheets of boPET film, known as [[drafting film]]. The boPET sheets become legal documents from which copies or [[blueprint]]s are made. boPET sheets are more durable and can withstand more handling than [[bond paper]]. Although "[[whiteprint|blueprint]]" duplication has fallen out of use, mylar is still used for its archival properties, typically as a record set of plans for building departments to keep on file.
* [[Transparency (projection)|Overhead transparency film]] for [[photocopier]]s or [[laser printer]]s (boPET film withstands the high heat).
* Modern [[lithography]] printing plates aka "Pronto Plates" (boPET resists oil)

===Other===
{{unreferenced section|date=July 2025}}
* [[Balloon]]s, metallic balloons
* Route information signs, called [[rollsign]]s or destination blinds, displayed by public transport vehicles
* For materials in [[kite flying|kite]]s
* Covering [[glass]] to decrease probability of shattering
* In theatre effects such as [[confetti]]
* As the adhesive strip to attach the string to a [[teabag]]
* One of the many materials used as windsavers or valves for [[valved harmonica]]s
* On farmland and domestic gardens, highly reflective aluminized PET film ribbons are used to keep birds away from plants
* Measuring tape
* Protecting [[pinball]] machine playfields from wear
* Used in dentistry when restoring teeth with composite
* In [[nail polish]], as a coloured and finely shredded additive to create a glitter effect
* Numismatics{{Snd}}Storing coins for long periods of time. [[Polyvinyl chloride|PVC]] was previously used for this, but over long periods of time PVC can release chlorine, which reacts with the silver and copper in coins. BoPET does not have this problem.
* In fishing fly tying, metallized Mylar strips are sometimes wound around the hook shank for reflective striping or shimmer in certain patterns.
* Military uniform accoutrements are often accented by gold mylar, such as shoulder epaulets or shoulder knots. For example: US Army Officer's Mess Dress Uniform.

==See also==
*[[Kapton]]

==References==
{{Reflist}}

== External links ==
* ''History of Polymers & Plastics for Teachers''. by The American Chemistry Council [http://plastics.americanchemistry.com/Education-Resources/Hands-on-Plastics/Introduction-to-Plastics-Science-Teaching-Resources/History-of-Polymers-Plastics-for-Teachers.html (HTML format)] or [http://plastics.americanchemistry.com/Education-Resources/Hands-on-Plastics/Introduction-to-Plastics-Science-Teaching-Resources/Background-Information-for-Teachers.pdf (PDF format) - 1.9MB], which includes the "[[Recycling Symbol|chasing arrow]]" recycling symbols (PET is #1) and a description of plastics.
* [https://www.youtube.com/watch?v=4Jf_zA5VuGs An interesting toy] has been developed using boPET and a stick-shaped [[Van de Graaff generator]].

{{DuPont}}
{{Authority control}}

{{DEFAULTSORT:Bopet}}
[[Category:Dielectrics]]
[[Category:Plastics]]
[[Category:Polyesters]]
[[Category:Reflective building components]]
[[Category:Packaging materials]]
[[Category:Food packaging]]
[[Category:Terephthalate esters]]