Borosilicate is a kind of glass that contains silica & boron trioxide, which gives it more strength and durability than ordinary glass. It's a non-toxic material that maintains its integrity even in extreme temperatures like those in a microwave.
Another benefit of borosilicate is its safety, if it breaks, it tends to crack into larger pieces instead of shattering, making it a lot safer than shards of glass and easier to clean up.
