borosilicate glass
Borosilicate glass is the glass you can pour boiling water into and take from oven to countertop without it cracking. Where soda-lime glass swells and shrinks a lot with temperature, borosilicate barely moves, so a sudden temperature change does not build the stresses that shatter ordinary glass. That single virtue, a low thermal-expansion coefficient, makes it the standard material for laboratory glassware, kitchen ovenware, and any glass that must survive thermal shock. It is sold under trade names like Pyrex and Duran.
The name gives away the trick: it adds boric oxide B2O3 to the silica. Boron is itself a network former, so instead of breaking the network the way soda does, it becomes part of it, joining the silica skeleton as its own oxygen triangles and keeping the glass highly connected. A typical composition is about 80 percent SiO2, 13 percent B2O3, 4 percent Na2O, and 2 percent Al2O3, with far less network-breaking soda than soda-lime glass. Because the network stays largely intact, the thermal-expansion coefficient drops to around 3.3 x 10^-6 per degree C, roughly a third that of soda-lime glass. Less expansion means less mismatch stress, means far better thermal-shock resistance.
Nothing comes free. Keeping the network intact keeps the glass viscous, so borosilicate melts and softens at higher temperatures and demands hotter furnaces and faster working than soda-lime glass, which makes it more expensive to produce. That cost is worth paying for labware, pharmaceutical vials, high-power lighting, and the huge cast blanks used for telescope mirrors, where dimensional stability against temperature swings is everything. For the ultimate in low expansion you go all the way to fused silica; borosilicate is the practical, affordable middle ground.
The 200-inch Hale telescope mirror was cast from borosilicate glass for exactly this reason: a mirror that changes shape as the night air cools would blur every star. Low-expansion borosilicate holds its curve as the temperature drifts. The same property, on a kitchen scale, is why a Pyrex dish goes from a hot oven onto a cool counter without the ting-and-crack a soda-lime dish would give.
Adding boron as a second network former gives borosilicate its low expansion and its resistance to thermal shock.
Not all modern kitchen ovenware labelled Pyrex is borosilicate; some is tempered soda-lime glass, which resists thermal shock by pre-stress rather than by low expansion and can behave differently in a sudden temperature change.