Pyrex - Wikiwand

Pyrex (trademarked as PYREX and pyrex) is a brand of glassware originally developed by Corning Incorporated. Pyrex was first introduced in 1915 as a line of clear, low-thermal-expansion borosilicate glass whose resistance to chemicals, electricity, and heat made it ideal for laboratory glassware and kitchenware. In the 1930s Corning expanded the brand to include kitchen products made of soda–lime glass and other materials.^[1]

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.

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History

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Corning Glass Works

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.^[2]

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.^[2] 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.^[3]

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.^[4] 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.

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.^[5]^[6] Corelle took over production of Pyrex and other Corningware products in the United States.^[7]

In 2019 Corelle Brands merged with Instant Brands, the makers of the Instant Pot.^[8] 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.^[9] 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.^[10]^[11]

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.^[12] 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.^[13]

A lawsuit by the State of Pennsylvania against Centre Lane Partners that attempted to halt the factory closure was dismissed by a federal judge.^[12] After months of uncertainty and multiple temporary closures, Anchor Hocking permanently closed the Charleroi factory in April 2025.^[14]

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^[15] to own rights to the brand in Europe, the Middle East and Africa.^[16]^[17] 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.^[18]

Arc International sold off its Arc International Cookware division including Pyrex business in 2014, and the division was subsequently renamed the International Cookware group.^[19] London-based private equity firm Kartesia^[20] purchased International Cookware in 2020.^[21]

In 2021, International Cookware acquired Pyrex rival Duralex for €3.5 million (US$4.2m).^[22]^[23]^[24]

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Trademark

Pyrex remains a trademark of Corning Incorporated, but is licensed by dinnerware manufacturers.^[25]

Corning Incorporated continues to manufacture PYREX (all uppercase) laboratory glassware for international markets.^[25] The pyrex (all lowercase, introduced in 1975^[26]) trademark is now used for kitchenware sold in the United States, South America, and Asia.^[27]

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^[28] for bakeware that has been made of numerous materials including borosilicate and soda–lime glass, stoneware, metal, plus vitroceramic cookware.^[29]

It is a common misconception that the logo style alone indicates the type of glass used to manufacture the bakeware.^[30] In reality, Corning's introduction of soda-lime-glass-based Pyrex in the 1940s predates the introduction of the all lowercase logo by nearly 30 years.^[31]^[26]^[32]

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Composition

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Older clear-glass Pyrex manufactured by Corning, Arc International'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.^[33]^[34]

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.^[35] The composition of both Corning 7740 and Schott 8330 is given as 80.6% SiO₂, 12.6% B₂O₃, 4.2% Na₂O, 2.2% Al₂O₃, 0.1% CaO, 0.1% Cl, 0.05% MgO, and 0.04% Fe₂O₃.

In the late 1930s and 1940s, Corning also introduced new product lines under the Pyrex brand using different types of glass. Opaque tempered soda–lime glass was used to create decorated opal ware bowls and bakeware, and aluminosilicate glass was used for Pyrex Flameware stovetop cookware. The latter product had a bluish tint caused by the addition of alumino-sulfate.^[36]^[37]

Beginning in the 1980s, production of clear Pyrex glass products manufactured in the USA by Corning was also shifted to tempered soda–lime glass, like their popular opal bakeware.^[31] This change was justified by stating that soda–lime glass has higher mechanical strength than borosilicate—making it more resistant to physical damage when dropped, which is believed to be the most common cause of breakage in glass bakeware. The glass is also cheaper to produce and more environmentally friendly. Its thermal shock resistance is lower than borosilicate's, leading to potential breakage from heat stress if used contrary to recommendations. Since the closure of the soda–lime plant in England in 2007, European Pyrex has been made solely from borosilicate.^[7]^[38]^[39]

The differences between Pyrex-branded glass products has also led to controversy regarding safety issues—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.^[40] They admitted their testing conditions were "contrary to instructions" provided by the manufacturer.^[37]^[41] 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."^[38]

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Use in telescopes

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 200-inch (5.1 m) telescope mirror for the California Institute of Technology's Palomar Observatory project.^[42] 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.^[43] 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.^[44]