What is Bullet-proof glass?
[[File:Bulletproof glass window after a burglary attempt.jpg|thumb|right|220px|Bulletproof glass of a jeweller's window after some people tried to rob the store.]] [[File:IDET2007 bulletproof glass armor.jpg|thumb|right|220px|Ballistic test of a bullet-resistant glass panel]] '''Bullet-proof glass''', or bullet-resistant glass, is a type of strong, clear material that resists [[bullet]]s. Complete protection against all [[weapon]]s is not possible. It is usually made from two or more types of [[material]], one hard and one soft. The softer layer makes the glass more [[elastic]], so it can flex (bend) instead of shatter. There must be a clear view through the glass. Bulletproof glass varies in thickness from three-quarters of an inch to three inches.<ref>Bertino AJ & Bertino PN 2008. ''Forensic Science: fundamentals and investigations''. Cengage Learning. 407</ref> A popular method is stick a special [[plastic]] film to the inner surface of ordinary glass. This 'security laminate' bonds to the glass with an [[adhesive]]. This gives a protection similar to the multi-layered bullet-resistant glass. [[Transparency]] is better, tint-free; thickness and weight is reduced as much as 50-70%. The laminate can be stuck on to existing windows; this a called a 'retrofit'. == Methods == === The concept === The plastic provides little bullet-resistance. Glass, much harder than plastic, flattens the bullet. The plastic deforms, absorbing [[energy]] and (perhaps) stopping the bullet. The ability of the plastic layer to stop projectiles is directly proportional to its thickness.<ref>Gunnarsson C.A. ''et al.'' 2009. Deformation and failure of polycarbonate during impact as a function of thickness. ''Proceedings of the Society for Experimental Mechanics (SEM) Annual Conference''. Albuquerque, New Mexico</ref> Bulletproof glass may be up to three inches thick. === The materials === All the parts of the glass must be [[transparent]]. The essential components are these: # A very hard substance # A softer plastic that can bend und