{{Short description|Brand of glassware}} {{Distinguish|PUREX}} {{For-multi|the programming language|Pyrex (programming language)|the rapper|Pyrex (rapper)}} {{Use American English|date=May 2026}} {{Use mdy dates|date=May 2026}} [[File:Pyrex 1-quart liquid measuring cup - DPLA - b07e5efc0a37cf693d74b366a3065c72.jpg|thumb|A PYREX 1-quart measuring cup manufactured after 1940, featuring graduations in United States customary units]]
'''Pyrex''' (trademarked as ''PYREX'' and ''pyrex'') is a type of borosilicate glass developed by Corning Incorporated in 1908. Pyrex was first introduced to the public in 1915, as a brand of clear, low-thermal-expansion glassware products, whose resistance to chemicals, electricity, and heat made it ideal for laboratory glassware and kitchenware.<ref name= "A Brief History of Pyrex">{{cite web|url= https://www.foodandwine.com/lifestyle/kitchen/history-of-pyrex |title= A Brief History of Pyrex |author= Nina Friend |publisher= Food & Wine |date= 26 January 2026|access-date= 27 February 2026 }}</ref><ref name= "The Beginning of Pyrex">{{cite web|url= https://pyrex.cmog.org/content/beginning-pyrex |title= The Beginning of Pyrex |author= Regan Brumagen |publisher= Corning Museum of Glass |date= |access-date= 27 February 2026 }}</ref> In the 1930s, Corning expanded the brand to include kitchen products made of soda–lime glass and other materials.
In 1998, Corning Incorporated spun off its kitchenware division, including Pyrex cookware. Currently, Pyrex dishes are manufactured by Corelle Brands in the United States and International Cookware in Europe. Corning Incorporated continues to manufacture Pyrex scientific glassware.<ref>{{cite web |title=Laboratory Glassware |url=https://www.corning.com/worldwide/en/products/life-sciences/products/glassware.html |website=corning.com |publisher=Corning Incorporated |access-date=10 March 2026}}</ref>
== History == ===Corning Glass Works=== thumb|upright|alt=A black and white advert for Pyrex entitled "You Really Can't Get Along Without This Pyrex Biscuit Dish".|1915 Pyrex advertisement
Borosilicate glass was first made by German chemist and glass technologist Otto Schott, founder of Schott AG in 1893.
In 1908, Eugene Sullivan, director of research at Corning Glass Works, developed Nonex, a borosilicate low-expansion glass, to reduce breakage in shock-resistant lantern globes and battery jars. Sullivan had learned about Schott's borosilicate glass as a doctoral student in Leipzig, Germany.<ref name="IDSAQuote">[http://www.industrialdesignhistory.com/node/137 Corning Pyrex Bakeware] {{Webarchive|url=https://web.archive.org/web/20171208054145/http://www.industrialdesignhistory.com/node/137 |date=2017-12-08 }}, Carroll M. Gantz, Design Chronicles: Significant Mass-produced Designs of the 20th Century, Schiffer Publications, Ltd. 2005</ref>
[[File:Erlenmeyer flask ben.jpg|thumb|left|A series of Pyrex Erlenmeyer flasks]]
Jesse Littleton of Corning discovered the cooking potential of borosilicate glass by giving his wife Bessie Littleton a casserole dish made from a cut-down Nonex battery jar. Corning removed the lead from Nonex and developed it as a consumer product.<ref name="IDSAQuote"/> Pyrex made its public debut in 1915 during World War I and was positioned as an American-made alternative to Duran.
The material was initially marketed for pie pans and advertised as "Pie Right" or "Py-Right", but the name was eventually changed to Pyrex to rhyme with Nonex.<ref>{{cite journal |last1=William B. |first1=Jensen |title=The Origin of Pyrex |journal=Journal of Chemical Education |date=May 2006 |volume=83 |issue=5 |page=692 |doi=10.1021/ed083p692 |url=https://ia600108.us.archive.org/view_archive.php?archive=/24/items/wikipedia-scholarly-sources-corpus/10.1021%252Fcr990402t.zip&file=10.1021%252Fed083p692.pdf}}</ref> A Corning executive gave the following account of the etymology of the name "Pyrex":{{blockquote|The word PYREX is probably a purely arbitrary word which was devised in 1915 as a trade-mark for products manufactured and sold by Corning Glass Works. While some people have thought that it was made up from the Greek {{transliteration|grc|pyr}} and the Latin {{lang|la|rex}}, we have always taken the position that no graduate of Harvard would be guilty of such a classical hybrid. Actually, we had a number of prior trade-marks ending in the letters ''ex''. One of the first commercial products to be sold under the new mark was a pie plate, and in the interests of euphonism the letter r was inserted between ''pie'' and ''ex'' and the whole thing condensed to PYREX.<ref>{{cite journal | journal = American Speech | volume = 32 | issue = 4 | year = 1957 | page = 290 | title = title unknown | last = Mathews | first = MM}}</ref>}}Corning purchased the Macbeth-Evans Glass Company in 1936 and their Charleroi, Pennsylvania plant was used to produce Pyrex opal ware bowls and bakeware made of tempered soda–lime glass.<ref>{{Cite web |title=Macbeth-Evans Glass Company {{!}} ArchivesSpace Public Interface |url=https://archivesspace.cmog.org/agents/corporate_entities/20 |access-date=2022-10-16 |website=archivesspace.cmog.org}}</ref> In 1958 an internal design department was started by John B. Ward. He redesigned the Pyrex ovenware and Flameware. Over the years, designers such as Penny Sparke, Betty Baugh, Smart Design, TEAMS Design, and others have contributed to the design of the line. alt=A 2-cup pyrex measuring jug manufactured by Corelle.|thumb|A 2-cup ''pyrex'' measuring jug manufactured by Corelle.
===Corelle Brands=== In 1998 Corning Incorporated divested itself of its consumer products division, which was renamed World Kitchen in 2000, and Corelle Brands in 2018.<ref>{{cite news| url=http://www.the-leader.com/article/20140616/news/140619641| title=World Kitchen plans layoffs at Corning plant| last=Ek| first=Derrick| newspaper=The Leader| location=Corning NY| access-date=2021-02-12| language=en| archive-date=2023-08-15| archive-url=https://web.archive.org/web/20230815204141/https://www.the-leader.com/article/20140616/news/140619641| url-status=live}}</ref><ref>{{cite news| url=https://www.kitchenwarenews.com/world-kitchen-changes-name-corelle-brands/| title=World Kitchen Changes Name to Corelle Brands| journal=Kitchenware News| date=February 5, 2018| language=en| access-date=2021-02-12| archive-date=2023-08-15| archive-url=https://web.archive.org/web/20230815203458/https://www.kitchenwarenews.com/world-kitchen-changes-name-corelle-brands/| url-status=live}}</ref> Corelle took over production of Pyrex and other Corningware products in the United States.<ref name="History">{{cite web |url=http://www.pyrexware.com/thetruthaboutpyrex/manu.htm |title=Manufacturing History |publisher=Pyrex Products |access-date=5 June 2015|archive-url=https://web.archive.org/web/20111002090834/http://www.pyrexware.com/thetruthaboutpyrex/manu.htm|archive-date=2 October 2011}}</ref>
In 2019 Corelle Brands merged with Instant Brands, the makers of the Instant Pot.<ref>{{Cite news |last=Gottfried |first=Miriam |date=March 3, 2019 |title=Owners of Instant Pot, Corelle to Merge; Combined company would have enterprise value of more than $2 billion |work=The Wall Street Journal |url=https://www.wsj.com/articles/owners-of-instant-pot-corelle-to-merge-11551654000 |access-date=June 23, 2023 |archive-date=June 23, 2023 |archive-url=https://web.archive.org/web/20230623171037/https://www.wsj.com/articles/owners-of-instant-pot-corelle-to-merge-11551654000 |url-status=live }}</ref> The combined company filed for Chapter 11 bankruptcy in 2023 after high interest rates and waning access to credit hit its cash position and made its debts unsustainable.<ref>{{Cite web|url=https://finance.yahoo.com/news/instant-pot-pyrex-maker-instant-204114763.html|title=Instant Pot and Pyrex Maker Instant Brands Files for Bankruptcy|date=June 12, 2023|access-date=June 12, 2023|website=Yahoo Finance|language=en|archive-date=June 13, 2023|archive-url=https://web.archive.org/web/20230613003613/https://finance.yahoo.com/news/instant-pot-pyrex-maker-instant-204114763.html|url-status=live}}</ref> The company emerged from bankruptcy after the appliance portion (Instant Brands) and the housewares portion (Corelle Brands) of the business were separately purchased by private equity firm Centre Lane Partners, one of the largest stockholders in Pyrex rival Anchor Hocking.<ref>{{Cite press release |last=Brands |first=Instant |title=Instant Brands Provides Update on Sale Process for its Appliance Business |url=https://www.prnewswire.com/news-releases/instant-brands-provides-update-on-sale-process-for-its-appliance-business-301982393.html |access-date=2024-03-21 |website=www.prnewswire.com |language=en |archive-date=2024-03-21 |archive-url=https://web.archive.org/web/20240321031701/https://www.prnewswire.com/news-releases/instant-brands-provides-update-on-sale-process-for-its-appliance-business-301982393.html |url-status=live }}</ref><ref>{{Cite web |date=2024-03-01 |title=Instant Brands emerges from chapter 11 as Corelle Brands {{!}} Davis Polk |url=https://www.davispolk.com/experience/instant-brands-emerges-chapter-11-corelle-brands |access-date=2024-03-21 |website=www.davispolk.com |language=en}}</ref>
After the purchase was finalized in early 2024, Centre Lane transferred ownership of Corelle to Anchor Hocking. This arrangement came into public awareness later in the year after Anchor Hocking announced that they planned to close Pyrex's 132-year old factory in Charleroi, Pennsylvania, and relocate production to Anchor Hocking's factory in Lancaster, Ohio.<ref name = USD>{{cite web |title=Case 2:24-cv-01501-NR |url=https://www.govinfo.gov/content/pkg/USCOURTS-pawd-2_24-cv-01501/pdf/USCOURTS-pawd-2_24-cv-01501-0.pdf |website=govinfo.gov |publisher=United States District Court for the Western District of Pennsylvania|date=November 14, 2024}}</ref> Senators Bob Casey Jr. and John Fetterman each criticized the move and demanded an explanation for how the merger of two major competitors was able to proceed without Federal Trade Commission oversight.<ref>{{cite news |last1=Anselmo |first1=Joelle |title=Pennsylvania glass plant closure sparks outrage |url=https://www.manufacturingdive.com/news/anchor-hocking-charleroi-pennsylvania-glass-pyrex-plant-closure-senators/728703/ |work=Manufacturing Dive |publisher=Informa TechTarget |date=October 7, 2024 |archive-date=August 31, 2025 |access-date=December 4, 2025 |archive-url=https://web.archive.org/web/20250831192723/https://www.manufacturingdive.com/news/anchor-hocking-charleroi-pennsylvania-glass-pyrex-plant-closure-senators/728703/ |url-status=live }}</ref>
A lawsuit by the State of Pennsylvania against Centre Lane Partners that attempted to halt the factory closure was dismissed by a federal judge.<ref name = USD/> After months of uncertainty and multiple temporary closures, Anchor Hocking permanently closed the Charleroi factory in April 2025.<ref>{{cite news |last1=Wells |first1=Anna |title=132-Year-Old Pyrex Plant Closes for Good After Four Shutdown Delays |url=https://www.ien.com/video/video/22938488/132yearold-pyrex-plant-closes-for-good-after-four-shutdown-delays |work=Industrial Equipment News |publisher=Industrial Media, LLC |date=April 14, 2025 |archive-date=April 29, 2025 |access-date=December 4, 2025 |archive-url=https://web.archive.org/web/20250429141707/https://www.ien.com/video/video/22938488/132yearold-pyrex-plant-closes-for-good-after-four-shutdown-delays |url-status=live }}</ref>
===European history=== After Corning Incorporated divested itself of its consumer products division in 1998, Newell Cookware Europe retained its license to produce Pyrex in Europe, Africa, and the Middle East.
France-based cookware maker Arc International acquired Newell's European business in early 2006<ref name="hoovers">{{cite web | url = http://www.hoovers.com/arc-international/--ID__103296--/free-co-factsheet.xhtml | title = Arc International page |publisher = Hoover's | access-date = 5 June 2015|archive-url=https://web.archive.org/web/20070929140533/http://www.hoovers.com/arc-international/--ID__103296--/free-co-factsheet.xhtml|archive-date=29 September 2007}}</ref> to own rights to the brand in Europe, the Middle East and Africa.<ref>{{cite book | isbn = 978-1-84685-556-6 | title = The Little Book of Collectable British Pyrex | first = Susan | last = Hibberd | publisher = Exposure Publishing | year = 2007 }}</ref><ref>{{cite web | url = http://www.arc-international-cookware.com/en_Glass_Ovenware.html | title = Glass Ovenware | publisher = Arc International | access-date = 2008-03-17 | year = 2005 |archive-url = https://web.archive.org/web/20080311222706/http://www.arc-international-cookware.com/en_Glass_Ovenware.html <!-- Bot retrieved archive --> |archive-date = 2008-03-11}}</ref> In 2007, Arc closed the Pyrex soda–lime factory in Sunderland, UK moving all European production to France. The Sunderland factory had first started making Pyrex in 1922.<ref>{{Cite web|url=https://www.bbc.co.uk/insideout/northeast/series11/week7_pyrex.shtml|title=BBC Inside Out -|website=www.bbc.co.uk|access-date=2025-09-16|archive-date=2025-04-17|archive-url=https://web.archive.org/web/20250417064236/https://www.bbc.co.uk/insideout/northeast/series11/week7_pyrex.shtml|url-status=live}}</ref>
Arc International sold off its Arc International Cookware division including Pyrex business in 2014, and the division was subsequently renamed the International Cookware group.<ref>{{Cite press release|url=https://www.prnewswire.com/news-releases/aurora-capital-group-completes-acquisition-of-arc-international-cookware-243487371.html|title=Aurora Capital Group Completes Acquisition of Arc International Cookware|website=PR Newswire|access-date=2020-04-05|archive-date=2020-10-20|archive-url=https://web.archive.org/web/20201020072230/https://www.prnewswire.com/news-releases/aurora-capital-group-completes-acquisition-of-arc-international-cookware-243487371.html|url-status=live}}</ref> London-based private equity firm Kartesia<ref>{{cite web |title=Jaime Prieto - Kartesia |url=https://informaconnect.com/superreturn-international/speakers/jaime-prieto/ |access-date=16 November 2021 |website=informaconnect.com |language=en |archive-date=16 November 2021 |archive-url=https://web.archive.org/web/20211116202654/https://informaconnect.com/superreturn-international/speakers/jaime-prieto/ |url-status=live }}</ref> purchased International Cookware in 2020.<ref>{{cite web |title=Aurora Resurgence has sold International Cookware to Kartesia |url=https://www.lincolninternational.com/transactions/aurora-resurgence-has-sold-international-cookware-to-kartesia/ |access-date=16 November 2021 |website=Lincoln International LLC |language=en |archive-date=16 November 2021 |archive-url=https://web.archive.org/web/20211116202655/https://www.lincolninternational.com/transactions/aurora-resurgence-has-sold-international-cookware-to-kartesia/ |url-status=live }}</ref>
In 2021, International Cookware acquired Pyrex rival Duralex for €3.5 million (US$4.2m).<ref>{{Cite web |last=AFP |date=2021-01-29 |title=French glassmaker Duralex purchased by rival |url=https://www.dawn.com/news/1604250 |access-date=2021-01-29 |website=DAWN.COM |language=en |archive-date=2021-01-29 |archive-url=https://web.archive.org/web/20210129061628/https://www.dawn.com/news/1604250 |url-status=live }}</ref><ref>{{cite web |title=Pyrex completes acquisition of Duralex |url=https://www.glass-international.com/news/pyrex-completes-acquisition-of-duralex |access-date=16 November 2021 |website=Glass International |language=en |archive-date=16 November 2021 |archive-url=https://web.archive.org/web/20211116202654/https://www.glass-international.com/news/pyrex-completes-acquisition-of-duralex |url-status=live }}</ref><ref>{{cite web |last1=Whitten |first1=Zoe |date=31 January 2021 |title=International Cookware, Pyrex's parent company, takes over Duralex |url=https://www.glassonline.com/international-cookware-pyrexs-parent-company-takes-over-duralex/ |access-date=16 November 2021 |website=Glass Online |archive-date=26 March 2023 |archive-url=https://web.archive.org/web/20230326210323/https://www.glassonline.com/international-cookware-pyrexs-parent-company-takes-over-duralex/ |url-status=live }}</ref>
== Trademark == Pyrex remains a trademark of Corning Incorporated, but is licensed by two dinnerware manufacturers.<ref name = pvp>{{cite web |title=PYREX vs. pyrex: What's the Difference? |url=https://www.corning.com/worldwide/en/products/life-sciences/resources/stories/in-the-field/pyrex-vs-pyrex-whats-the-difference.html |website=corning.com |publisher=Corning Incorporated |access-date=4 December 2025 |archive-date=8 November 2025 |archive-url=https://web.archive.org/web/20251108032759/https://www.corning.com/worldwide/en/products/life-sciences/resources/stories/in-the-field/pyrex-vs-pyrex-whats-the-difference.html |url-status=live }}</ref><ref name=":2">{{Cite web |date=2020-02-17 |title=Difference between Pyrex® USA and Pyrex®Europe |url=https://international-cookware.zendesk.com/hc/en-gb/articles/360011862740-Difference-between-Pyrex-USA-and-Pyrex-Europe |access-date=2026-02-15 |website=Pyrex® Help Center |language=en-GB |archive-date=2025-10-13 |archive-url=https://web.archive.org/web/20251013235620/https://international-cookware.zendesk.com/hc/en-gb/articles/360011862740-Difference-between-Pyrex-USA-and-Pyrex-Europe |url-status=live }}</ref>
thumb|Pyrex logo as used by Corelle
Corning Incorporated continues to manufacture '''PYREX''' (all uppercase) laboratory glassware for international markets.<ref name = pvp/> The '''pyrex''' (all lowercase, introduced in 1975<ref name=":1">{{Cite web |title=Pyrex 1975 Dealer Catalog. Corning, N.Y: Corning Glass Works |url=https://cmog.primo.exlibrisgroup.com/discovery/fulldisplay?&context=L&vid=01CORNING_INST:01CORNING_INST&search_scope=MyInstitution&tab=ALWAYS_DISPLAY&docid=alma991233953504126 |access-date=2022-11-20 |website=cmog.primo.exlibrisgroup.com |language=en |archive-date=2022-11-20 |archive-url=https://web.archive.org/web/20221120213859/https://cmog.primo.exlibrisgroup.com/discovery/fulldisplay?&context=L&vid=01CORNING_INST:01CORNING_INST&search_scope=MyInstitution&tab=ALWAYS_DISPLAY&docid=alma991233953504126 |url-status=live }}</ref>) trademark is now used for kitchenware sold in the United States, South America, Asia, and Australia.<ref name=":2" /> thumb|Pyrex logo as used by International Cookware In Europe, Africa, and the Middle East, a variation of the PYREX (all uppercase) trademark is licensed by International Cookware.<ref name=":2" /><ref>{{Cite web |title=Kartesia participates in the {{as written|aqu|isition [sic]}} of International Cookware, the leading kitchenware manufacturer under the Pyrex® brand in EMEA |url=https://www.kartesia.com/newsroom/new_deal_international_cookware |access-date=2023-06-23 |website=www.kartesia.com |language=en |archive-date=2023-06-23 |archive-url=https://web.archive.org/web/20230623171039/https://www.kartesia.com/newsroom/new_deal_international_cookware |url-status=live }}</ref>
== Composition == thumb|right|alt=Two clear measuring jugs featuring red text. The jug on the right is wider than the jug on the left.| A clear tempered ''pyrex'' soda–lime glass measuring jug produced by Instant Brands (left, differentiated by its different logo and bluish tint), and a clear borosilicate glass ''PYREX'' measuring jug produced by Corning (right)
Older clear-glass Pyrex manufactured by Corning, International Cookware's Pyrex products, and Pyrex laboratory glassware are made of borosilicate glass. According to the National Institute of Standards and Technology, borosilicate Pyrex is composed of (as percentage of weight): 4.0% boron, 54.0% oxygen, 2.8% sodium, 1.1% aluminium, 37.7% silicon, and 0.3% potassium.<ref>{{cite web | publisher = National Institute of Standards and Technology | title = Composition of Pyrex Glass | access-date = September 8, 2016 | url = http://physics.nist.gov/cgi-bin/Star/compos.pl?matno=169 | archive-date = September 26, 2020 | archive-url = https://web.archive.org/web/20200926021553/http://physics.nist.gov/cgi-bin/Star/compos.pl?matno=169 | url-status = live }}</ref>
According to glass supplier Pulles and Hannique, borosilicate Pyrex is made of Corning 7740 glass and is equivalent in formulation to Schott Glass 8330 glass sold under the "Duran" brand name.<ref>{{cite web | url = http://www.pulleshanique.com/02_borosilicate-glass.htm | title = Borosilicate glass | access-date = 5 June 2015|archive-url=https://web.archive.org/web/20120315092729/http://www.pulleshanique.com/02_borosilicate-glass.htm|archive-date=15 March 2012}}</ref> The composition of both Corning 7740 and Schott 8330 is given as 80.6% {{chem2|SiO2|link=silicon dioxide}}, 12.6% {{chem2|B2O3|link=boron trioxide}}, 4.2% {{chem2|Na2O|link=sodium oxide}}, 2.2% {{chem2|Al2O3|link=aluminium oxide}}, 0.1% {{chem2|CaO|link=calcium oxide}}, 0.1% {{chem2|Cl|link=chlorine}}, 0.05% {{chem2|MgO|link=magnesium oxide}}, and 0.04% {{chem2|Fe2O3|link=iron(III) oxide}}.
Starting around the 1950s, Corning began making Pyrex out of thermally tempered soda–lime glass, instead of borosilicate glass, due to lower manufacturing costs.<ref>{{Cite web |last=Logan |first=Liz |title=How Pyrex Reinvented Glass For a New Age |url=https://www.smithsonianmag.com/innovation/how-pyrex-reinvented-glass-new-age-180955513/ |access-date=2026-02-15 |website=Smithsonian Magazine |language=en |archive-date=2024-08-26 |archive-url=https://web.archive.org/web/20240826235218/https://www.smithsonianmag.com/innovation/how-pyrex-reinvented-glass-new-age-180955513/ |url-status=live }}</ref> Some plants moved to tempered soda–lime formulations, while others continued to produce borosilicate Pyrex.<ref name=":3">{{Cite web |title=Are dishes that have the Pyrex stamp with all capital letters made with borosilicate glass? - Ask a Glass Question |url=https://libanswers.cmog.org/faq/398431 |access-date=2026-02-15 |website=libanswers.cmog.org |archive-date=2026-02-14 |archive-url=https://web.archive.org/web/20260214203510/https://libanswers.cmog.org/faq/398431 |url-status=live }}</ref> Herb Dann, a designer at Corning from 1961 to the 1990s, noted that by the time the consumer products division was sold in 1998, Corning had mostly switched to soda–lime glass for "almost all" of its tableware products.<ref name=":3" /> The exception to this was the 13"×9"×2" pan, which was never produced with soda–lime.<ref name=":3" />
Phil Ross, an independent consultant to the glass industry, whose clients included World Kitchen, said in 2008 that the U.S. industry as a whole switched in the 1980s from borosilicate to soda–lime owing to it being easier to melt and work with, as well as being more environmentally friendly due to lower emissions from the glass furnace used. He noted it was not economical for companies to install multi-million dollar filter systems.<ref name=":0">{{cite web |last1=Butterworth |first1=Trevor |date=14 October 2009 |title=Exploding the exploding Pyrex rumor |url=http://stats.org/stories/2009/exploding_pyrex_oct14_09.html |archive-url=https://web.archive.org/web/20141120095647/http://stats.org/stories/2009/exploding_pyrex_oct14_09.html |archive-date=20 November 2014 |access-date=5 June 2015 |website=STATS |publisher=Statistical Assessment Service}}</ref> This change was justified by stating that soda–lime glass has higher mechanical strength than borosilicate{{emdash}}it has around twice the strength{{emdash}}making it more resistant to physical damage when dropped, which is believed to be the most common cause of breakage in glass bakeware. However, its thermal shock resistance is lower than borosilicate's, leading to potential breakage from heat stress if used contrary to recommendations.<ref name=":0" /> Borosilicate's shock resistance is around three times higher than soda–lime.<ref name=":4">{{Cite journal |last=Bradt |first=R.C. |last2=Martens |first2=R.L. |date=September 2012 |title=Shattering glass cookware |url=https://rroeder.nd.edu/assets/387776/glasscookware.pdf |journal=American Ceramic Society |volume=91 |issue=7 |pages=36 |archive-url=https://web.archive.org/web/20251210140718/https://rroeder.nd.edu/assets/387776/glasscookware.pdf |archive-date=10 December 2025}}</ref>
<div class="center"> {|class="wikitable" |+Calculations of thermal differential, ∆T, for soda lime silicate and borosilicate glass. !Source !∆T Soda lime silicate !∆T Pyrex borosilicate |- |Bradt and Martens<ref name=":4" /> |~55°C (99°F) |~183°C (330°F) |- |Carter and Norton<ref>{{Cite book |last=Carter |first=C.B. |title=Ceramic Materials, Science and Engineering |last2=Norton |first2=M.G. |date=2007 |publisher=Springer |year=2007 |isbn=978-0-387-46271-4 |edition=1 |pages=633}}</ref> |~80°C (144°F) |~270°C (436°F) |- |Corning brochure<ref>{{Cite web |title=Wayback Machine |url=http://catalog2.corning.com/Lifesciences/media/pdf/Thermal_Properties_of_Corning_Glasses.pdf |archive-url=https://web.archive.org/web/20131109071848/http://catalog2.corning.com/Lifesciences/media/pdf/Thermal_Properties_of_Corning_Glasses.pdf |archive-date=2013-11-09 |access-date=2026-02-15 |website=catalog2.corning.com}}</ref> |~16°C (29°F) |~54°C (97°F) |} </div>
The differences between Pyrex-branded glass products has also led to controversy regarding safety issues{{emdash}}in 2008, the U.S. Consumer Product Safety Commission reported it had received 66 complaints by users reporting that their Pyrex glassware had shattered over the prior ten years yet concluded that Pyrex glass bakeware does not present a safety concern. The consumer affairs magazine ''Consumer Reports'' investigated the issue and released test results, in January 2011, confirming that borosilicate glass bakeware was less susceptible to thermal shock breakage than tempered soda lime bakeware.<ref>{{Cite web|url=https://gizmodo.com/the-pyrex-glass-controversy-that-just-wont-die-1833040962|title=The Pyrex Glass Controversy That Just Won't Die|last=Estes|first=Adam Clark|date=March 16, 2019|website=Gizmodo|language=en-US|access-date=2019-03-22|archive-date=2019-03-21|archive-url=https://web.archive.org/web/20190321205358/https://gizmodo.com/the-pyrex-glass-controversy-that-just-wont-die-1833040962|url-status=live}}</ref> They admitted their testing conditions were "contrary to instructions" provided by the manufacturer.<ref name="Snopes">{{cite web |date=18 September 2009 |title=Exploding Pyrex, Urban Legend reference |url=http://www.snopes.com/food/warnings/pyrex.asp |access-date=2011-01-08 |publisher=Snopes.com}}</ref><ref>{{cite web|title=FOIA requests examine glass bakeware that shatters|url=http://news.consumerreports.org/safety/2010/12/foia-requests-examine-glass-bakeware-that-shatters-.html?EXTKEY=I91CONL&CMP=OTC-ConsumeristLinks|publisher=Consumer Reports|access-date=7 February 2012|archive-url=https://web.archive.org/web/20111206025207/http://news.consumerreports.org/safety/2010/12/foia-requests-examine-glass-bakeware-that-shatters-.html?EXTKEY=I91CONL&CMP=OTC-ConsumeristLinks|archive-date=6 December 2011}}</ref> STATS analyzed the data available and found that the most common way that users were injured by glassware was via mechanical breakage, being hit or dropped, and that "the change to soda lime represents a greater net safety benefit."<ref name="History" /><ref name="Aikins">{{cite web |last=Aikins |first=Jim |title=Setting the Record Straight: The Truth About PYREX |url=http://www.pyrexware.com/thetruthaboutpyrex/index.htm |archive-url=https://web.archive.org/web/20111026114654/http://www.pyrexware.com/index.asp?pageId=30 |archive-date=26 October 2011 |access-date=5 June 2015 |publisher=Pyrex Products}}</ref><ref name=":0" /><ref>[http://consumerist.com/2010/12/consumer-reports-breaks-a-lot-of-glass-investigating-shattering-pyrex.html Consumer Reports Breaks A Lot Of Glass Investigating Shattering Pyrex Bakeware] {{Webarchive|url=https://web.archive.org/web/20120514061947/http://consumerist.com/2010/12/consumer-reports-breaks-a-lot-of-glass-investigating-shattering-pyrex.html|date=2012-05-14}}, The Consumerist</ref>
=== Distinguishing soda–lime and borosilicate Pyrex === It is a common misconception that the logo style alone indicates the type of glass used to manufacture the bakeware.<ref>{{Cite web |date=2023-02-27 |title=That Viral 'PYREX' Brand Hack Is Horseshit, Folks |url=https://lifehacker.com/that-viral-pyrex-brand-hack-is-horseshit-folks-1850157381 |access-date=2023-08-26 |website=Lifehacker |language=en |archive-date=2023-08-26 |archive-url=https://web.archive.org/web/20230826214203/https://lifehacker.com/that-viral-pyrex-brand-hack-is-horseshit-folks-1850157381 |url-status=live }}</ref> In reality, Corning's introduction of soda–lime based Pyrex in the 1940s predates the introduction of the all lowercase logo by around 30 years, which first appeared in 1975.<ref name=":1" /><ref name="Aikins" /> Additionally, the transition to soda–lime was not uniform, as some plants continued to produce borosilicate pieces for a period of time, though was generally phased out by 1998.<ref name=":3" /> This means any Pyrex manufactured in the U.S. from the 1940s to 1998 could be either borosilicate or soda–lime, regardless of the capitalization of the logo. The Corning Museum of Glass website summarizes: "The short answer is that the change from upper to lower case signified a re-branding of the trademark Pyrex® in the late 1970s but is not a conclusive way to determine, historically, what type of glass formulation the product is made from."<ref name=":3" />
==== Visual differences ==== When asked about any visual differences, Corning designer Herb Dann noted in a 2014 interview: "Actually, the tempered [soda-lime] is a little bluer glass, it can alter the color of it. In fact, at one time we actually had a straw color in all of the Pyrex line. Today when you walk into the company store, it's all blue and that's a cheaper glassmelt because they're not purifying, they're not taking the cobalt out. So it's a cheaper melt, but it's all tempered lime."<ref>{{Cite AV media |url=https://www.youtube.com/watch?v=CESW46j0ins |title=Herb Dann Session 2: Rakow Research Library Conversation Series |date=2015-05-01 |last=Corning Museum of Glass |access-date=2026-02-15 |via=YouTube |archive-date=2025-08-16 |archive-url=https://web.archive.org/web/20250816074440/https://www.youtube.com/watch?v=CESW46j0ins |url-status=live }}</ref> The U.S. Pyrex website notes: "You may notice that some of our Pyrex® brand glassware has a slight tint of green or blue hue to the dish. It is not a coating or added color. It comes from the raw materials in the glass itself. The blue comes from adding cobalt to the raw materials. This does not affect the performance of the dish; it is purely cosmetic."<ref>{{Cite web |title=Frequently Asked Questions |url=https://pyrexhome.com/pages/frequently-asked-questions |access-date=2026-02-15 |website=Pyrex Home |language=en |archive-date=2025-10-06 |archive-url=https://web.archive.org/web/20251006002425/https://pyrexhome.com/pages/frequently-asked-questions |url-status=live }}</ref>
==== U.S. post–1998 ==== From 1998, World Kitchen (Later Corelle Brands, then Anchor Hocking) used the Corning soda–lime formulation at their plant in Charleroi, Pennsylvania.<ref name="Aikins" /> The plant was shut down in April 2025, after 132 years of operation.<ref>{{Cite AV media |url=https://www.ien.com/video/video/22938488/132yearold-pyrex-plant-closes-for-good-after-four-shutdown-delays |title=132-Year-Old Pyrex Plant Closes for Good After Four Shutdown Delays |date=2025-04-14 |language=en-us |access-date=2026-02-15 |via=www.ien.com |archive-date=2025-04-29 |archive-url=https://web.archive.org/web/20250429141707/https://www.ien.com/video/video/22938488/132yearold-pyrex-plant-closes-for-good-after-four-shutdown-delays |url-status=live }}</ref> Production was then shifted to Lancaster, Ohio by new owners Anchor Hocking.<ref>{{Cite web |title=As Charleroi’s glassmaking tradition ends, an Ohio town gains from its loss |url=https://www.post-gazette.com/business/career-workplace/2024/12/08/anchor-hocking-pyrex-glass-charleroi-lancaster/stories/202412040087 |access-date=2026-02-15 |website=Pittsburgh Post-Gazette |language=en |archive-date=2026-01-10 |archive-url=https://web.archive.org/web/20260110071446/https://www.post-gazette.com/business/career-workplace/2024/12/08/anchor-hocking-pyrex-glass-charleroi-lancaster/stories/202412040087 |url-status=live }}</ref> Ultimately, production of all U.S. Pyrex since 1998 has been made of soda–lime glass with the lowercase logo.<ref name=":5">{{Cite web |last=Shaw |first=Natasha |title=We just found out there's a difference between PYREX and pyrex |url=https://www.taste.com.au/articles/we-just-found-out-theres-difference-between-pyrex-pyrex-you-dont-want-mix-them-up/sv69srpd |url-status=live |access-date=15 February 2026 |website=Taste.com.au}}</ref>
==== England ==== In 1921, James A Jobling acquired the licence to produce Pyrex in the UK. The original kiln was replaced with a borosilicate furnace to create the Pyrex.<ref name=":6">{{Cite web |date=October 2015 |title=CORNING’S GLASSWORKS, LISBURN TERRACE, SUNDERLAND TYNE AND WEAR Final Excavation Report |url=https://eprints.oxfordarchaeology.com/5576/1/Lisburn_Terrace_Complete.pdf |archive-url=https://web.archive.org/web/20240812062457/https://eprints.oxfordarchaeology.com/5576/1/Lisburn_Terrace_Complete.pdf |archive-date=12 August 2024 |access-date=15 February 2026 |website=oxfordarchaeology.com}}</ref> Production started in 1922 at his Sunderland factory in England, and continued for over 50 years. In 1973, the licence expired, and Corning took control of the factory and the Jobling company.<ref>{{Cite web |title=Pyrex plate in Chelsea Design. {{!}} Science Museum Group Collection |url=https://collection.sciencemuseumgroup.org.uk/objects/co8668363/pyrex-plate-in-chelsea-design |access-date=2026-02-15 |website=collection.sciencemuseumgroup.org.uk |language=en |archive-date=2025-08-17 |archive-url=https://web.archive.org/web/20250817150131/https://collection.sciencemuseumgroup.org.uk/objects/co8668363/pyrex-plate-in-chelsea-design |url-status=live }}</ref><ref>{{Cite web |title=BBC Inside Out - |url=https://www.bbc.co.uk/insideout/northeast/series11/week7_pyrex.shtml |access-date=2026-02-15 |website=www.bbc.co.uk |archive-date=2025-04-17 |archive-url=https://web.archive.org/web/20250417064236/https://www.bbc.co.uk/insideout/northeast/series11/week7_pyrex.shtml |url-status=live }}</ref><ref>{{Cite news |last=Hammer |first=Alexander R. |date=1973-05-12 |title=Corning Glass Takes Control Of Two Companies in Britain |url=https://www.nytimes.com/1973/05/12/archives/corning-glass-takes-control-of-two-companies-in-britain-river.html |access-date=2026-02-15 |work=The New York Times |language=en-US |issn=0362-4331 |archive-date=2025-07-10 |archive-url=https://web.archive.org/web/20250710104112/https://www.nytimes.com/1973/05/12/archives/corning-glass-takes-control-of-two-companies-in-britain-river.html |url-status=live }}</ref> Pyrex produced before Corning took over was stamped with a "JAJ" symbol.<ref>{{Cite web |title=The Agee Story: Identifying pyrex items with markings |url=http://www.ageestory.info/identifying_marked.html |access-date=2026-02-15 |website=www.ageestory.info |archive-date=2025-08-17 |archive-url=https://web.archive.org/web/20250817135856/http://www.ageestory.info/identifying_marked.html |url-status=live }}</ref> Production at the facility took place until 2007 when it was shut down, and production of Pyrex was shifted to France.<ref>{{Cite web |date=2007-01-18 |title=Glassmaker announces plan to close Wearside factory |url=https://www.thenorthernecho.co.uk/business/1130169.glassmaker-announces-plan-close-wearside-factory/ |access-date=2026-02-15 |website=The Northern Echo |language=en}}</ref> All Pyrex made at the factory was borosilicate.<ref name=":6" />
==== France ==== Production in France began in 1922 with the glassblowers Clovis and Léon Régent at the Bagneaux-sur-Loing glassworks. Production continued for several years until the factory was relocated to Châteauroux in 1970 where it continues as of 2026.<ref>{{Cite web |title=history - Pyrex® Webshop EU |url=https://www.pyrex.eu/en-eu/pages/history |access-date=2026-02-15 |website=www.pyrex.eu |language=en |archive-date=2025-10-16 |archive-url=https://web.archive.org/web/20251016225845/https://www.pyrex.eu/en-eu/pages/history |url-status=live }}</ref> All Pyrex made at the factory is borosilicate with the uppercase logo.<ref name=":2" /><ref name=":5" />
==== Australia ==== Australian Pyrex is distributed by Corelle Brands, who offer the lowercase soda–lime glass.<ref name=":7">{{Cite web |title=Pyrex Support |url=https://globalkitchenbrands.com.au/pages/pyrex-support |access-date=2026-02-15 |website=Global Kitchen Brands Australia Pty Ltd |language=en |archive-date=2025-10-06 |archive-url=https://web.archive.org/web/20251006050427/https://globalkitchenbrands.com.au/pages/pyrex-support |url-status=live }}</ref><ref>{{Cite web |title=Pyrex - Official Australia Online Store - Buy Pyrex Measuring Cups, Small & Large Bowls, Storage, Cookware, & More |url=https://globalkitchenbrands.com.au/collections/pyrex |access-date=2026-02-15 |website=Global Kitchen Brands Australia Pty Ltd |language=en |archive-date=2025-10-10 |archive-url=https://web.archive.org/web/20251010100123/https://globalkitchenbrands.com.au/collections/pyrex |url-status=live }}</ref> However, they also offer the French-made borosilicate glass.<ref name=":7" /><ref>{{Cite web |title=PYREX® Iconics Mixing Bowl 1.1L |url=https://globalkitchenbrands.com.au/products/pyrex-originals-glass-mixing-bowl-1l-1030236 |access-date=2026-02-15 |website=Global Kitchen Brands Australia Pty Ltd |language=en |archive-date=2025-07-11 |archive-url=https://web.archive.org/web/20250711190558/https://globalkitchenbrands.com.au/products/pyrex-originals-glass-mixing-bowl-1l-1030236 |url-status=live }}</ref> Additionally, borosilicate glass with the lowercase logo is offered in the "Bake N Serve" and "Cook N Serve" ranges which are produced in China.<ref name=":5" /><ref>{{Cite web |title=Pyrex® Bake N Serve Rectangle Baker-1.6L |url=https://globalkitchenbrands.com.au/products/pyrex-bake-n-serve-16l-rectangle-baker |access-date=2026-02-15 |website=Global Kitchen Brands Australia Pty Ltd |language=en |archive-date=2026-02-15 |archive-url=https://web.archive.org/web/20260215044738/https://globalkitchenbrands.com.au/products/pyrex-bake-n-serve-16l-rectangle-baker |url-status=live }}</ref><ref>{{Cite web |title=Pyrex® Cook N Serve Casserole 2.1L |url=https://globalkitchenbrands.com.au/products/pyrex-cook-n-serve-casserole-21l |access-date=2026-02-15 |website=Global Kitchen Brands Australia Pty Ltd |language=en |archive-date=2026-02-15 |archive-url=https://web.archive.org/web/20260215045108/https://globalkitchenbrands.com.au/products/pyrex-cook-n-serve-casserole-21l |url-status=live }}</ref>
Previously, Pyrex was produced in Australia by Crown Crystal Glass from 1926.<ref name=":8">{{Cite web |title=Australian PYREX Reference Guide |url=https://thatretropiece.com/pages/australian-pyrex-reference-guide |access-date=2026-03-22 |website=That Retro Piece |language=en}}</ref> Many pieces were labelled with various stamps, or lacking stamps entirely.<ref name=":8" /> Stamps used included "Crown Agee Pyrex" in the mid 1960s, "Agee Pyrex" until 1969–70, "Crown Ovenware" in the mid 1970s, "Pyrex Ovenware" in the mid to late 1970s and "Pyrex Australia" in the late 1970s and 1980s.<ref name=":8" /> Crown Crystal Glass also distributed Pyrex-branded goods sourced from the United Kingdom and United States.<ref name=":8" />
== Patterns and collecting == alt=A white oval dish decorated with stylized orange, red and black flowers with a clear lid.|thumb|Pyrex casserole dish with the 'Toledo' pattern Pyrex has achieved somewhat of a cult following<ref name=":9">{{Cite web |title=A Guide to the Most Rare Vintage Pyrex – Estate Sale Blog |url=https://estatesales.org/thegoods/a-guide-to-the-most-rare-vintage-pyrex |access-date=2026-03-22 |language=en-US}}</ref> through its various colours and patterns produced after World War II,<ref>{{Cite web |title=Pattern Library {{!}} Pyrex |url=https://pyrex.cmog.org/pattern-library |access-date=2026-03-22 |website=pyrex.cmog.org}}</ref> lending itself to collectors.<ref name=":9" /><ref name=":10">{{Cite web |last=Coldiron |first=Roxanna |date=20 January 2026 |title=A Guide to Collecting Vintage Pyrex—Plus, How Much It's Worth |url=https://www.marthastewart.com/7692706/collecting-vintage-pyrex |website=Martha Stewart}}</ref> Some valuable patterns include the 1956 Pink Daisy or the 1983 Colonial Mist.<ref name=":10" /> Depending on condition, prices can range from $100 for single pieces to $500 for a collection, according to flea market expert Nicolas Martin.<ref name=":10" /> Some pieces have sold for several thousand dollars on eBay.<ref name=":11">{{Cite web |date=2025-02-28 |title=7 of the Most Valuable Vintage Pyrex Dishes That Are Worth Collecting |url=https://www.mentalfloss.com/food/most-valuable-vintage-pyrex |access-date=2026-03-22 |website=Mental Floss |language=en-US}}</ref> Uncommon shapes or limited-run productions also affect the value of the pieces.<ref name=":9" /><ref name=":11" />
== Use in telescopes == [[File:Hale telescope mirror during grinding 1945.jpg|thumb|alt=A black and white photograph of a large, flat mirror with a geometric pattern, supported on a metal frame with several people surrounding it.|Pyrex glass used on the mirror of the Hale Telescope]]
Because of its low expansion characteristics, borosilicate glass is often the material of choice for reflective optics in astronomy applications.
In 1932, George Ellery Hale approached Corning with the challenge of fabricating the {{convert|200|in|m|adj=on}} telescope mirror for the California Institute of Technology's Palomar Observatory project.<ref name="glassgiant">{{cite web |title=The Glass Giant |url=http://www.cmog.org/article/glass-giant |archive-url=https://web.archive.org/web/20160120080037/http://www.cmog.org/article/glass-giant |archive-date=2016-01-20 |access-date=30 January 2015 |website=Corning Museum of Glass}}</ref> A previous effort to fabricate the optic from fused quartz had failed, with the cast blank having voids. The mirror was cast by Corning during 1934–1936 out of borosilicate glass.<ref name = Caltech>{{cite web|title=A History of Palomar Observatory|url=http://www.astro.caltech.edu/palomar/about/history.html|website=Palomar Observatory|publisher=California Institute of Technology|access-date=5 June 2015|date=28 May 2015|archive-date=26 May 2015|archive-url=https://web.archive.org/web/20150526181759/http://www.astro.caltech.edu/palomar/about/history.html|url-status=live}}</ref> After a year of cooling, during which it was almost lost to a flood, the blank was completed in 1935. The first blank now resides in the Corning Museum of Glass.<ref>{{cite web|title=200-inch Disk|url=https://glasscollection.cmog.org/objects/41284/200inch-disk|publisher=Corning Museum of Glass|access-date=30 January 2015|archive-date=24 December 2023|archive-url=https://web.archive.org/web/20231224100441/https://glasscollection.cmog.org/objects/41284/200inch-disk|url-status=live}}</ref>
==Gallery== <gallery mode="packed"> File:Chocolate cake and ice cream.jpg|A Pyrex plate manufactured in the 1960s File:Pyrex dish.jpg|A vintage Pyrex roaster File:Pyrexette Kit.jpg|A 1925 Pyrex glass baking dish set for children File:Museum of Glass Pyrex exhibit - panoramio.jpg|Pyrex exhibit in the Corning Museum of Glass </gallery>
==See also== * Jena glass * Borosilicate glass * Gorilla Glass
{{Clear}}
== Citations == {{Reflist}}
== General and cited references == * {{Cite journal |last1=Bradt |first1=R. C. |last2=Martens |first2=R. L. |date=September 2012 |title=Shattering Glass Cookware |url=https://bulletin-archive.ceramics.org/is-cacheable/1605850352249/ucuifj.pdf |url-access=subscription |journal=American Ceramic Society Bulletin |volume=91 |issue=7 |pages=35–41 |issn=0002-7812 |oclc=302290362 |access-date=15 March 2024}} ** {{Cite press release |last=DeGuire |first=Ellen |date=September 11, 2012 |title=New Paper Addresses Causes of Shattering Glass Cookware; Margin of Safety Described as 'Borderline' |url=http://ceramics.org/uncategorized/new-paper-addresses-causes-of-shattering-glass-cookware |publisher=American Ceramic Society |access-date=2012-09-17 |quote=Their investigation confirmed the borosilicate glass would withstand a much larger rapid temperature change. According to their calculation and those of others, soda lime glass cookware shatters more frequently because, in theory, it can only resist fracture stress for temperature differentials less than about 55 °C (99 °F). In contrast, they estimate that the borosilicate glassware could tolerate a temperature differential of about 183 °C (330 °F), a three-fold difference.}} * {{Cite book |last=Gantz |first=Carroll |year=2001 |title=Design Chronicles: Significant Mass-produced Products of the 20th Century |location=Atglen, PA |publisher=Schiffer Publishing |isbn=978-0-7643-2223-5 |oclc=58729534}} * {{Cite book |last1=Rogove |first1=Susan Tobier |first2=Marcia B.|last2=Steinhauer |year=1993 |title=Pyrex by Corning: A Collector's Guide |location=Marietta, Ohio |publisher=Antique Publications |isbn=0-915410-94-X |oclc=28440879}} * {{Cite book |last1=Rogove |first1=Susan Tobier |year=2016 |title=More Pyrex by Corning: A Collector's Guide |others=Photography: Jay Kogut Photography |location=Pennsauken, NJ |publisher=BookBaby |isbn=978-1-4835-8646-5 |oclc=963732418}}
== External links == {{Commons category|Pyrex}} * {{Official website|https://www.pyrex.com/}} * [http://www.Pyrexlove.com Pyrex Love], a vintage Pyrex reference site
{{Glass makers and brands|state=collapsed}} {{Authority control}}
Category:American brands Category:Boron compounds Category:Corning Inc. Category:Glass trademarks and brands Category:Kitchenware brands Category:Kitchenware Category:Low-expansion glass Category:Products introduced in 1915 Category:Companies that filed for Chapter 11 bankruptcy in 2023 Category:Transparent materials