What improvements have been made to bullet proof glass?

For years it has been known that the glass is resistant and that it resists impacts of hard objects, it is spoken of the bulletproof glass. For this research, there are years of study and technological advances that help determine whether bulletproof glass actually exists and whether this resistance exists. Durable crystals have been manufactured with higher layers of resistance and power to resist bullets, for some this bullet-proof glass does not exist, for others, it has already existed for years.