Typical forward flight station window is made up of six (6) layers.
Starting from the outside these layers are:
1] Glass faceplate.
2] Window heat film.
3] Layer of Polyvinyl Butyral (PVB).
4] Layer of Stretched Acrylic.
5] Second layer of PVB.
6] Second layer of Stretched Acrylic.
The outer glass layer is non-structural but provides an abrasion resistant surface for the wipers and a surface for attaching the window heat film.