Bulletproof glass

Bullet-resistant glass is constructed using polycarbonate, thermoplastic, and layers of laminated glass. The aim is to make a material with the appearance and clarity of standard glass but with effective protection from small arms. Polycarbonate designs usually consist of products such as Armormax, Makroclear, Cyrolon, Lexan or Tuffak, which are often sandwiched between layers of regular glass. The ability of a glass itself to withstand shock is improved by the process of tempering. When treated with heating and cooling or with chemical processes, the glass becomes much stronger. The polycarbonate usually has one of two types of coating to resist abrasion: a soft coating that heals after being scratched (such as elastomeric carbon-based polymers) or a hard coating that prevents scratching (such as silicon-based polymers). The plastic in laminate designs also provides resistance to impact from physical assault from blunt and sharp objects. The plastic provides little in the way of bullet-resistance. The glass, which is much harder than plastic, flattens the bullet, and the plastic deforms, with the aim of absorbing the rest of the energy and preventing penetration. The ability of the polycarbonate layer to stop projectiles with varying energy is directly proportional to its thickness, and bulletproof glass of this design may be up to 3.5 inches thick.

Laminated glass layers are built from glass sheets bonded together with polyvinyl butyral, polyurethane or ethylene-vinyl acetate. This design has been in regular use on combat vehicles since World War II. It is typically thick and is usually extremely heavy.