Glass can be replaced with many different substances. Often, when glass is replaced with a different substance, plastic is the generally picked. The two most popular glass substitutes are called Plexiglas and Lexan. Plexiglas is breakable but only under extreme force making it very useful for many applications.
When Plexiglas does break though, it breaks similarly to tempered glass: into very tiny salt-like pieces that prevent one from being cut. The other substitute is called Lexan. Lexan is an extremely powerful plastic even stronger than Plexiglas. Lexan has been used in many different applications. Lexan is used on some windshields, space and sport helmets, Ferraris, and even bullet resistant windows.
There are both upsides and downsides to glass substitutes, particularly: Glass substitutes that are made of plastic are great for strength and durability, but because these glass substitutes are made of plastic they are more flexible. In high winds these Plexiglas and Lexan windows will shake and make noise unlike glass. Glass is the preferred choice when a substitute isn’t really necessary.