Beginning in the 1980s, production of clear Pyrex glass products manufactured by Corning (and later Instant Brands, after the consumer division was spun off and renamed) was also shifted to tempered soda-lime glass, like their popular opal bakeware.[22] This change was justified by stating that soda-lime glass has higher mechanical strength than borosilicate—making it more resistant to physical damage when dropped, which is believed to be the most common cause of breakage in glass bakeware. The glass is also cheaper to produce and more environmentally friendly. However, its thermal shock resistance is lower than borosilicate’s, leading to potential breakage from heat stress if used contrary to recommendations. Since the closure of the soda-lime plant in England in 2007, European Pyrex has been made solely from borosilicate.[4][23][24]
The differences between Pyrex-branded glass products has also led to controversy regarding safety issues—in 2008, the U.S. Consumer Product Safety Commission reported it had received 66 complaints by users reporting that their Pyrex glassware had shattered over the prior ten years yet concluded that Pyrex glass bakeware does not present a safety concern. The consumer affairs magazine Consumer Reports investigated the issue and released test results, in January 2011, confirming that borosilicate glass bakeware was less susceptible to thermal shock breakage than tempered soda lime bakeware.[25] However, they admitted their testing conditions were “contrary to instructions” provided by the manufacturer.[21][26] STATS analyzed the data available and found that the most common way that users were injured by glassware was via mechanical breakage, being hit or dropped, and that “the change to soda lime represents a greater net safety benefit.”[23]
Though I imagine that cost might also be a factor.
https://en.wikipedia.org/wiki/Pyrex
Though I imagine that cost might also be a factor.