Popular Science Magazine online just featured an article today regarding current Pyrex and why the glass is not as heat resistant as it used to be, thus more prone to shattering with drastic change in temperature. Old Pyrex used to made from borosilicate glass but now it's made from soda lime glass. Soda lime glass is actually stronger than borosilicate glass though less resistant to heat. It's considered stronger because it's less resistant to shattering upon dropping. Interestingly, US Pyrex is the only one that made the switch to soda lime. England, for example, still uses borosilicate.
They Sure Don't Make Pyrex Like They Used to
Another interesting fact: Apparently, Pyrex used to be utilized in the illegal production of crack cocaine but, in 1998 when they sold Pyrex to World Kitchen and they changed the components of the glass, it became more difficult for dealers and makers to make crack! They had to go and buy Pyrex science glassware which is still made the old way.
Enjoy your weekends!