What is Pyrex?

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Pyrex refers to a brand which is launched in 1915 by Corning Incorporated. This brand sells clear borosilicate glasses with low thermal expansion. This type of glassware is normally utilized inside laboratories and may also serve as kitchenware.

Presently, Corning Incorporated no longer produces and sells Pyrex-branded glassware for kitchens and laboratories in the United States. However, Pyrex borosilicate glass products are still made under different companies. Instead of borosilicate, World Kitchen, LLC made use of tempered soda-lime glass for their various products.

The National Institute of Standards and Technology states that the original borosilicate Pyrex is made up of boron, silicon, oxygen, aluminium, potassium, and sodium. On the other hand, Pulles and Hannique which is a supplier of glass, states that borosilicate Pyrex is composed of Corning 7740 glass which is similar in composition to the Schott Glass 8830 glass. Corning 7740 and Schott Glass 8830 are made up of silicon dioxide, boron trioxide, sodium oxide, aluminium oxide, Iron (III) oxide, calcium oxide, magnesium oxide, and chlorine.

According to World Kitchen, they made use of soda-lime glass for their Pyrex kitchenware because it is much cheaper to manufacture and possesses a greater mechanical strength compared to borosilicate. Having a high level of mechanical strength means that it doesn’t break easily when it is dropped. However, compared to borosilicate Pyrex glassware, tempered soda-lime glass is not as heat resistant. With this, there is an increase in terms of breakage of products that is due to heat stress.

Because there are variations in Pyrex products depending on the company that manufactured them, the Consumer Product Safety Commission has received various reports in 2010 regarding their Pyrex glassware. Most of these consumer complaints state that their glassware had been broken when subjected to high temperatures. However, based on the investigation of Consumer Reports magazine, these complainants have been using products made up of tempered flint glass and have wrongly assumed that these have the same properties as borosilicate glassware.