American Pyrex Less Resistant to Thermal Shock
December 11, 2010 8:38 AM Subscribe
Flying Shards of Hot Glass.
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Reports of consumer injuries
led Consumer Reports to investigate the safety of glass bakeware. It turns out that US-made Pyrex glass bakeware is no longer as resistant to thermal shock as it used to be, nor as resistant as European-made Pyrex still is.
Pyrex glass bakeware was originally made
from borosilicate glass, a material whose resistance to breakage due to changes in temperature
was so strong that it was used in railyards for lantern glass. Now, however, Pyrex
(and main competitor Anchor Hocking
) are made from a less expensive material: soda lime glass that has been strengthened through thermal tempering.
European-made Pyrex is still made from borosilicate glass, which enabled Consumer Reports to test brand-new samples of each type of glass, side-by-side, for resistance to thermal shock. "We baked at least five samples
of each brand in a 450-degree oven. All of the U.S. Pyrex and Anchor dishes shattered when placed on the wet countertop. None of the European dishes made of borosilicate broke, except one practice-run Arcuisine Elegance dish that had been through two baking cycles in our lab."
In its defense, Pyrex says
that given the number of its products in use, the number of reported injuries is small, and also that soda lime glass is more resistant to impact breakage, which is a more common cause of injuries. (Consumer Reports found the resistance to impact breakage to vary widely among samples, but that some samples of soda lime glass were in fact quite strong in that regard.)
Some advice for safer usage.