Tomas,
If you want it really thin, go with microscope slide cover glass. The beauty of cover glass is that it's glass - i.e. it's inert, won't react to any adhesive, won't discolor nor fog up. All you need to do is to cut it to shape.
Tom
https://tstage9.wixsite.com/nyc-modeling
Time...It marches on...without ever turning around to see if anyone is even keeping in step.
I've used the clear plastic that the modular components are packaged in.
Another option is a product called Micro Glaze available from Micro Mark. It is applied as a white liquid inside the individual panes and then dries to a clear finish. It creates an old time wavy glass look. It is recommended for panes 1/4" or smaller although I have had trouble with panes that large. The liquid often bursts before curing. I've had no such trouble with panes 1/8".
I want to replace the plastic window glass that comes in some Walters building kits with thinner material. Any suggestions would be appreciated . TOMAS