What does borosilicate mean?
Borosilicate is primarily known as a noun denoting a special type of glass made from silica and boric oxide. The addition of boron gives the material remarkably low thermal expansion, which means it can withstand sudden temperature changes — moving from freezer to oven, or from flame to cold rinse — without shattering. For this reason borosilicate glass became the standard for laboratory equipment such as beakers, flasks, and pipettes, and it is also widely used in bakeware, telescope mirrors, and high-quality drinkware. Chemically, the term can more broadly refer to salts or esters combining boric and silicic acid constituents, though this sense is largely confined to mineralogy and chemistry texts. In everyday conversation the word carries connotations of durability, scientific precision, and heat resistance, and it often appears in product descriptions as a mark of quality. Its most familiar brand association is Pyrex, though not all products sold under that name today contain true borosilicate glass.
nounA salt or ester of a hypothetical boric acid and silicic acid; specifically, a glass containing at least five percent boric oxide (B₂O₃), valued for its resistance to heat and chemical corrosion.
- A glass composed mainly of silica and boric oxide, prized for thermal shock resistance and used in laboratory ware and cookware.
- (In chemistry) any salt or ester derived from both boric and silicic acids.
"The laboratory beakers were made of borosilicate so they could withstand direct heating over a flame."
"Chemists prefer borosilicate flasks because they can be heated directly without cracking."
"The telescope's mirror was cast from low-expansion borosilicate to keep its shape as temperatures changed overnight."
Rarely pluralised; when used of the glass, 'borosilicate' typically appears as an uncountable material noun or as an attributive modifier ('a borosilicate flask'). The plural occurs mainly in mineralogy and chemistry when distinguishing different borosilicate compounds or minerals.
"Several rare borosilicates were identified in the rock sample."
That sturdy Pyrex dish in your kitchen and the flasks that survive open flames in chemistry labs share one secret ingredient: boric oxide, the magic behind borosilicate glass.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of borosilicate
The word borosilicate combines 'bor-', from borax, which traces back through Arabic būraq to Persian roots referring to the mineral, with '-silicate', derived from Latin silex, meaning flint or hard stone, the source of 'silica'. It emerged in nineteenth-century chemical nomenclature alongside related coinages such as 'borate' and 'silicate' as chemists systematically named salts of the various acids. The term gained widespread practical significance in the late nineteenth century after German chemist Otto Schott developed heat-resistant borosilicate glass, later popularised commercially through brands like Pyrex.
Related word forms
How borosilicate is actually used
Almost always used in technical or commercial registers — in materials science, laboratory supply catalogues, kitchenware marketing, and astronomy. In everyday speech people rarely say 'borosilicate' generically; they say 'Pyrex' or 'ovenproof glass', even though 'Pyrex' is a trademark and modern Pyrex sold in some countries may not actually be borosilicate.
Easily confused with borosilicate
A silicate is a compound of silicon and oxygen alone, whereas a borosilicate also incorporates boron compounds such as boric oxide.
A borate is a boron-containing compound without the silicon component found in borosilicates.