The Pyrex Glass Controversy That Just Won’t Die
17th March 2019
The vast majority of glass products are made of soda-lime glass: window panes, jars, bottles, all kinds of glass. Soda-lime glass is cheaper to make than borosilicate glass, which is undoubtedly why Pyrex started experimenting with it. However, borosilicate glass is not only harder, stronger, and more durable than soda-lime glass; it’s also more resilient to thermal shock. Thermal shock is what happens when a temperature change causes different parts of a material to expand at different rates, and the resultant stress can cause the material to crack. If the temperature change happens rapidly materials like glass can shatter or seem to explode. Resistance to thermal shock is part of why Pyrex became so popular for cookware; you could move a hot glass pan into a cool spot without worrying about it cracking or shattering. It’s also part of why laboratories prefer to use borosilicate glass rather than conventional soda-lime glass. Pyrex cookware currently sold in the United States goes through a thermal tempering process. In theory, this should strengthen the glass.
In practice, the difference between the performance of borosilicate glass and soda-lime glass is significant.