Borosilicate glass

Borosilicate glass is a type of glass with silica and boron trioxide as the main glass-forming constituents. Borosilicate glasses are known for having very low coefficients of thermal expansion (~3 × 10⁻⁶ K⁻¹ at 20 °C), making them resistant to thermal shock, more so than any other common glass. Such glass is less subject to thermal stress and is commonly used for the construction of reagent bottles. Borosilicate glass is sold under such trade names as Borcam, Borosil, Suprax, Simax, Heatex, Endural, Schott, Refmex, Kimble, and some (but not all) items sold under the trade name Pyrex.

Borosilicate glass was first developed by German glassmaker Otto Schott in the late 19th century. Otto Schott is also founder of today's SCHOTT AG, which has sold borosilicate glass under the brand name DURAN since 1893. Another manufacturer of is the DURAN Group. After Corning Glass Works introduced Pyrex in 1915, the name became a synonym for borosilicate glass in the English-speaking world. However, borosilicate glass is the name of a glass family with various members tailoring completely different purposes. Most common today is borosilicate 3.3 glass like SCHOTT Duran and Pyrex by Corning.

The European manufacturer of Pyrex, Arc International, uses borosilicate glass in its Pyrex glass kitchen products; however, the U.S. manufacturer of Pyrex kitchenware uses tempered soda-lime glass. Thus Pyrex can refer to either soda-lime glass or borosilicate glass when discussing kitchen glassware, while Pyrex, Bomex, Duran, TGI and Simax all refer to borosilicate glass when discussing laboratory glassware. The real difference is the trademark and the company that owns the Pyrex name. The original Corning ware made of borosilicate glass was trademarked in capital letters (PYREX). When the kitchenware division was sold, the trademark was changed to lowercase (pyrex) and switched to low thermal-expansion soda-lime glass. The bottom of new kitchenware and old kitchenware can be inspected for an immediate difference. The scientific division of Pyrex has always been using borosilicate glass.

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