In the wake of mass shootings and natural disasters, “security films” and after-market laminates continue to draw the attention of both media and consumers. While there are plenty of good security applications for these products–such as moderate anti-burglar protection and shatter-resistance for home windows in tornado-prone regions–stopping bullets and bomb attacks isn’t among them. For the time being, retrofit plastic films can’t impart meaningful ballistic security; you really do need actual bullet resistant glass if you want to reliably stop actual bullets.
SECURITY FILM AND BULLET PROOF GLASS
Security films are made from multi-ply sheets of biaxially-oriented polyethylene terephthalate (which sounds fancy, but is basically just a super-sturdy version of the plastic used to make soda bottles). In the case of a security film, the “grain” of the thermoplastic sheet is carefully oriented for optimum energy disbursement–something analogous to the way the nylon weave of a tennis racket is arranged, but on a molecular level. These energy-absorbing security films can be “glued” to existing windows.
This is similar, in theory, to what’s done when sheets of tempered glass are laminated together to make bullet resistant glass. But that process includes baking the layered glass in an autoclave to affix the laminate. These after-market security films–which cure at room temperature–are applied to a single layer of glass (which may or may not be tempered), and is ultimately something more akin to that of an auto-windshield than laminated bullet proof glass. The film will prevent shards of glass from flying–and often keeps the window intact–but it will not reliably prevent a projectile from penetrating the window.