And it's not just bakeware that's shattering. In the latest investigation, there were eight reports involving glass bowls and seven involving glass measuring cups. Some shattered when hot water was poured into them. And others shattered in the microwave when they were used to heat foods, even though they are labeled microwave-safe.
Pyrex and Anchor Hocking glass bakeware are now made of a type of glass called soda lime that has been heat strengthened. Decades ago they were made of borosilicate. Though it's not clear when the switch occurred, the manufacturers say soda lime is less likely to break when it's dropped or bumped. And they say it's equally resistant to temperature changes.
Consumer Reports laboratory tests compared the two types of glass bakeware. New pans were subjected to extreme heat then put on a wet granite countertop—conditions likely to cause breakage and contrary to the manufacturer's instructions.
Ten out of ten times the soda lime bakeware broke. But the borosilicate dishes did not break, though most did after baking at slightly higher temperatures.
When using glass pans, it's extremely important to follow safety precautions. Among the most important is to never place dishes on burners or under broilers, and be sure to place hot glassware on dry potholders. Or simply use metal pans in the oven.