This is probably a rather unusual question for this forum. The review of the movie Metropolis (made in 1926) by Roger Ebert shows what I assume is a still frame from the movie:
The shield looks very thin and has the typical small scratches that I would expect from a transparent thermoplastic.
My question: What material is this? If this is a silica-based glas and not a thermoplastic (did that exist in 1926?), what characteristics does it have? Is it flexible?