Since we're discussing windows, let's talk (BrE) double-glazing--i.e. having two panes of glass in a window in order to reduce noise and loss of heat. The AmE equivalent would be double-paned windows, but the AmE term is much less commonly heard term than its BrE equivalent since double-glazed/paned windows don't offer the same level of home improvement in the US as in the UK. I've never lived in a house in the US (I've lost count of how many) that didn't have windows that are structured to have two layers, and I've never lived in a house in the UK (I've lived in four) that had more than one layer of glass in a very (BrE) draughty/(AmE) drafty frame. But this is not to say that most American houses have double-paned/glazed windows--far from it. Instead, they have a window frame with two tracks, with a window permanently in the inner track and the option of a mesh (AmE and AusE) screen or a storm window (i.e. of glass or similar material) for the outer track. In the part of the country I'm from, where it's very, very cold in winter and very, very hot in summer, a spring ritual is to (AmE or BrE) swap/(BrE) swop the storm windows for screens, with a predictable reversal of ritual in the fall/autumn.
Incidentally, when I'm asked what (besides people) I miss about the US, window screens are in the top three. One cannot enjoy a breezy warm evening in England without sharing it with every moth, wasp and mosquito in the neighbo(u)rhood. (The other two in the top three, since I expect you'll ask, are electrical outlets in bathrooms and butter wrappers that are marked with measurements, for easy baking. Electrical outlets are definitely number one--the other two change position with the seasons.)
And as long as we're discussing materials that you can look through, the plastic stuff is called perspex (or Perspex) in BrE and plexiglass (or Plexiglas--or some other combination of capitalization and esses) in AmE. Both of these are originally proprietary names--and another AmE proprietary name for this kind of stuff is Lucite. (Though I'd use Lucite when it's a thicker, less flexible piece--such as in a paperweight or the like.)