Borosilicate glass is a medical-grade glass commonly used in the manufacture of glass sex toys, including dildos and anal plugs. It is made from a mix of sand, ground lime, soda and boron oxide. Pyrex is a well-known brand of borosilicate glass.
Borosilicate glass is lead-free and completely non-toxic. It can also withstand extreme temperatures and up to 3,000 pounds of pressure, so sex toys made from this material are incredibly durable, safe, long lasting, and resistant to bacteria.
Borosilicate glass is commonly referred to as hard glass.