What makes bulletproof glass bulletproof?

What makes bulletproof glass effective is its multi-layered, 'sandwich' construction and its ability to absorb and dissipate massive amounts of kinetic energy. Unlike a single pane of glass that shatters upon impact, bullet-resistant glass consists of several layers of glass and plastic (polycarbonate or acrylic) bonded together. When a bullet strikes the material, the hard outer layer of glass is designed to mushroom the bullet, flattening its tip and increasing its surface area. This initial impact begins to slow the projectile down. As the bullet travels through the subsequent layers of plastic, those layers act like a flexible net, stretching and absorbing the energy rather than breaking. The polycarbonate layers are particularly important because they are highly resilient and can bend without cracking. This process continues until the bullet’s energy is completely spent. The total thickness and the specific combination of materials determine the 'rating' of the glass, or how large of a bullet it can stop. Essentially, it’s a high-tech combination of hardness (to deform the bullet) and toughness (to absorb the shock) that provides the protection.