Clear plastic sheeting?

[Tom Line]

I've noticed that a LOT of teams use clear, thin plastic sheeting on their robots. Thin, but still very rigid, and clear (but still a bit flexible). Many teams used it this year to go around the outside of their spirals.

I want to call it acetal, or acetate - but when I went to look on mcmaster the sheer amount and variety of plastic sheeting made be scratch my head a bit. I know it isn't vinyl, which is not nearly as rigid and is quite heavy. So what's the right name for the thin semi-rigid plastic most teams use on their bots?

You can see it here on Foley Freeze on the outside of their spiral:
http://www.chiefdelphi.com/media/img...48d13528_l.jpg