The composite
Glass outer layers bonded to a polycarbonate core, usually with polyurethane interlayers that allow the two materials to expand and contract at different rates without delaminating.
Each material does the job it is best at:
- The outer glass face takes the environment — cleaning, grit, UV, weather. It is hard, clear and stable.
- The polycarbonate core takes the impact. It deforms and absorbs energy rather than fracturing, which is where the weight saving and the multi-hit performance come from.
- The inner layer contains spall, so nothing is thrown at whoever is standing behind the panel.
The problem it solves
Put the two simpler options side by side and each has one disqualifying weakness for a customer-facing position:
Laminated glass looks right and lasts, but it is heavy and it spalls.
Polycarbonate is light and does not spall, but it scratches in ordinary cleaning and yellows under UV.
A bank counter or a jewellery showroom front needs the glass surface and the no-spall behaviour. GCP is what that combination costs.
Where it earns its price
- Cash-handling counters — occupants directly behind the glass, and a surface the public sees
- Jewellery and watch showrooms — display glazing that is also the security boundary, and must stay pristine
- Reception and control positions — same combination at lower threat levels
- Rated opening panels — where weight matters and the panel is handled daily
Where it is over-specified
If the panel is a perimeter window with desks well back from it, spall is not a concern and laminated glass is the better value. If it is an interior screen with no UV exposure and low cleaning traffic, plain polycarbonate does the job for less.
We would rather specify the simpler build where the requirement is simpler.
Thermal and acoustic
GCP can be built into a sealed unit as one leaf — see insulated bullet-resistant units — so a rated opening need not be a thermal weak point.
Acoustically it performs well, as any thick laminated composite does, though a thick all-glass laminate generally edges it because of the mass.
Framing
The same rule as every build in the bullet-resistant range: the frame, glazing bead depth, fixings and any hardware are specified to the same rating as the panel. A rated panel in an unrated frame moves the weak point rather than removing it.
For whether ballistic glazing is the right answer at all, see bulletproof windows in Mumbai.