borosilicate

Borosilicate is a family of glass in which silica (SiO2) is combined with a considerable amount of boron trioxide (B2O3). The boron modifies the glass network, reducing the coefficient of thermal expansion and increasing thermal shock resistance while preserving clarity and chemical durability. Typical compositions include around 80–90% silica, 7–13% boron oxide, and small amounts of alkali and alkaline-earth oxides to adjust processing and properties.

The resulting material has a low coefficient of thermal expansion compared with common soda-lime glass, contributing to good thermal stability. It remains transparent over a wide temperature range and is resistant to many chemicals, though it is not immune to attack by hydrofluoric acid. Continuous-use temperatures for borosilicate glass are commonly in the few hundred degrees Celsius range, with short exposure to higher temperatures possible.

Borosilicate glass is manufactured by melting silica with boron oxide and additives, then forming and annealing the material. It is produced in a variety of forms, including tubing, rods, sheets, and finished labware. In industry and consumer markets, borosilicate glass is widely used for laboratory glassware, such as flasks, beakers, and test tubes, due to its chemical and thermal properties. It is also used in cookware and bakeware in many regions under brands such as Pyrex, although regional product formulations vary and some markets offer soda-lime alternatives.

Historically, borosilicate glass was developed in the late 19th to early 20th century by Otto Schott and became prominent in scientific applications in the 20th century. It is commonly categorized as a general-purpose borosilicate 3.3 glass, reflecting its low alkali content and favorable thermal characteristics.