Bullet RESISTENT FILMS
I Think your looking for a window tinting film known as 'security film'.
Google it, there are many manufacturers, none will promise "bullet proof".
It can actually stop a base ball bat or a fire axe on the first try. It's a very thick laminate with some extremely strong glue, and basically what it does is as the window is struck, it keeps the peices of tempered glass stuck to the film so it does not fall apart.
It's applied to the inside of the glass, and is by no means 'bullet proof'. The only substance I know of that is bullet proof is 3/4 to 1" thick lexan. There is a reason they retro fit politicians cars like a mercedes with this kind of thing. It's truly one of the only cars you can fit this type/thickness of lexan into stock doors. CP