Design & Make

Borosilicate Glass

by Sebastian Kaufmann November 21, 2009
ReadBorosilicate Glass

Humans started making glass about 5,000 years ago, which makes it one of the oldest manufactured materials in the world. However, major scientific breakthroughs in regards to glass didn’t come until the 19th century. In the 1880s, the German scientist Otto Schott (1851–1935) invented borosilicate glass, a new, much stronger variety of the material. He started selling it in 1893 under the name “Duran.” Schott still sells it under this name today. In the United States, borosilicate glass was first manufactured by Corning Glass Works in 1915, and sold under the name Pyrex.

Boron is the magic ingredient that makes borosilicate glass so exceptionally strong. It handles extreme temperature ranges (thermal insulation tiles on the Space Shuttle are coated with a borosilicate), and is chemically resistant — even to nuclear waste!  Needless to say, borosilicate glass is the standard for laboratory use.

All these qualities make borosilicate glass a perfect material for many kitchen utensils, both for its durability and visual appeal. It can be made almost impossibly thin. It feels so fragile in your hands that you distrust the science. See for example the Chemex Coffeemaker.

Boron / Photo by Images of Elements

Unfortunately, Pyrex, once synonymous with borosilicate glass, switched from borosilicate to soda-lime glass in the 1950s, with the majority of the U.S. kitchen industry following suit in the 1980s. Soda-lime glass is the most commonly used and least expensive form of glass. Another sad story in which the quest for lower prices led to the sacrifice of quality. Ironically, the European manufacturer of Pyrex, Arc International in France, still uses borosilicate glass in their Pyrex kitchen products today. So in order to get the original quality of an American icon, you have to buy it in France.

Since soda-lime glass extends more when subjected to heat, breakage of the glass is more likely. Pyrex’s answer to all this: “The Cookware Manufacturers Association considers soda lime an appropriate material for glass bakeware.” Of course, borosilicate glass also breaks under extreme conditions. But thanks to its singular quality, it is much more likely to crack or snap rather than shatter, making injuries less likely.

Today, you can still buy a good amount of borosilicate glassware for the kitchen (many manufacturers actually buy the glass in sheets from Schott).

Vintage Pyrex glass cooker, 1943. (Photo by

Leading image found at Chriftopher Chen via Flickr

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