Ok, I admit, this is nitpicking, but occasionally I feel the need to debunk this oft-repeated canard. Indulge me if you wish.
Originally, flasks and other laboratory glassware used for direct heating were made of borosilicate glass because it has far better thermal properties (less expansion, less prone to shatter from thermal shock) than soda lime glass. The drawback was that borosilicate glass is very brittle. Very old glassware can be dangerous because it breaks into large shards. When the state of the art progressed such that it was possible and economical to use toughened/tempered soda lime glass to make laboratory glassware, manufacturers switched. You will find that any flask that you order today will be tempered soda lime glass. This includes Kimax and Pyrex lines. You can confirm that it is tempered if you view it through a polarized lens because you can see the characteristic compressive strain lines in the glass.