Note that the above article is from 2011 and not particularly well-researched. Check out a bit more in-depth coverage on the issue from Snopes, including this interesting excerpt:
But do these complaints really chronicle problems with a substandard and possibly unsafe product, or do they merely constitute a relatively small roll call of consumer misuse incidents that have focused scrutiny on a single company? Some accounts (like the one reproduced above) have claimed that Pyrex brand products are now more prone to shattering than they used to be, attributing this increase to the factor that while Pyrex products were originally made of borosilicate glass, the company's products now vended in the North American market are fashioned of tempered soda lime glass, a cheaper material. (The borosilicate glass version is still sold in Europe.) While it is literally true that the material used in manufacturing Pyrex brand glass bakeware has changed from borosilicate glass to soda lime glass,
the brand's current owner, World Kitchen, claims that changeover began back in the 1940s and long antedates Corning's 1998 sale of the brand:
The Charleroi [Pennsylvania] plant has produced PYREX glass products out of a heat-strengthened (tempered) soda lime glass for about 60 years, first by our predecessor Corning Incorporated, and since 1998 by World Kitchen. In fact, since the 1980's, most, if not all consumer glass bakeware manufactured in the U.S. for consumers has been made of soda lime glass. Consumers should know that soda lime glass, such as that used to make PYREX glass bakeware, is significantly more resistant to breaking on impact than borosilicate glass and comparably resistant to breakage caused by severe temperature changes.
In a January 2011 article on glass bakeware, Consumer Reports stated that they were unable to determine exactly when major U.S. manufacturers (including Pyrex) switched from soda lime glass to borosilicate glass:
In the U.S. a major change occurred in the way glass bakeware was made. World Kitchen and Anchor Hocking now manufacture all of their glass bakeware using soda lime glass, which is less expensive to produce than borosilicate. Soda lime is commonly used in products such as drinking glasses and bottles.
It's not clear when the switch occurred. Anchor Hocking spokeswoman Barbara Wolf says borosilicate glass was phased out by the industry by the early 1980s. World Kitchen vice president Jim Aikins says Pyrex glass bakeware sold in the U.S. has consistently been made of soda lime glass that has been strengthened through thermal tempering at the Charleroi plant for about 60 years.
Sarah Horvath, a Corning spokeswoman, says Corning made Pyrex out of both soda lime and borosilicate at several locations before selling the U.S. business to World Kitchen in 1998, but provided no more details. P. Bruce Adams, formerly an executive scientist at Corning, says that borosilicate was still being used to make Pyrex when he retired in 1987.
Read more at
http://www.snopes.com/food/warnings/pyr ... 6beJlDD.99