This is a multilayer “sandwich” with  the glass facing outside and the poly as the inner surface: as the projectile proceeds the different layers act like a catcher’s mitt in slowing down the round and then physically catching it in one of the layers. This is why B4 glass is typically 21-24mm thick and B6 is  41-44 mm.

1. Glass with ceramic frit: This is the outer sheet of glass that looks very much like the original equipment glass in both shape and size.
2. PVB: This is the adhesive innerlayer between sheets of glass.
3. Glass:  Second sheet of glass.
4. PVB:  This is the adhesive inner layer between sheets of glass.
5. Glass:  Third sheet of glass.
6. PVB:  This is the adhesive inner layer between sheets of glass.
7. Glass:  Fourth and last sheet of glass. It is cut smaller and forms the
   channel that will innerlock with a similar mating hard armor frame surrounding the door.
8. Polyurethane:  This is the adhesive inner layer between glass and the polycarbonate which act as an anti spall shield.
9. Polycarbonate with abrasive resistant coating:  The polycarbonate acts as an antispall shield.

Are you are wondering what the bulge is???

The glass composition used by most major ballistic glass makers such as Isoclima
puts glass on the outside layer, several layers of glass and poly vinyl buteral in the middle, next polyurethane, and finally polycarbonate.

The benefit of this method is the ability
of the polycarbonate to expand and "catch" the fragments created by the harder glass surfaces. Expansion in excess of two inches is possible.

This is an example of a German DIN optics test on a windscreen. A special grid is projected through the windscreen at the same angle as a
driver would be viewing it. Any distortion in the glass will result in waviness of the lines projected on the screen. This waviness can be
measured and the optical quality of the glass determined in an objective and quantitative way. Looking through a distorted windscreen at night or in bright sunlight is similar to using the wrong prescription glasses. If the driver is distracted by poor optics, safety of the vehicle and passengers is compromised.

Visual acuity is crucial in everyday conditions and the results can be catastrophic under attack if not up to standard. As the defeat level
increases, so does the difficulty in manufacturing ballistic glass to Euronorm standards.

For nearly a decade only one glass manufacturer in the world has been able to consistently produce optically acceptable glass at Euronorm specifications that satisfies OEM standards. Most armoring firms do not even perform rudimentary transparent armor testing for clarity and distortion. Far West Consulting Group performs the testing at the glass manufacturing facility and at the plant to insure standards