The U.S. Air Force has developed a new form of bulletproof glass; using aluminum oxynitride, known as ALON. This stuff is stronger and lighter than current bulletproof glass. Both the current bulletproof glass, and ALON, use layers of material. The stuff in ALON is just thinner, lighter, tougher, and nearly impossible to scratch. That’s an important factor for glass in aircraft or combat vehicles, that is exposed to a lot of blowing sand, and is expected to last a while. Cost is a factor in this. Current types of bullet proof glass cost about three dollars per square inch, while AON costs about five times more. Being lighter and more durable, ALON is more likely to appear in aircraft first. That’s because ALON has already demonstrated in tests that it can stop multiple hits by medium (7.62mm) and heavy (12.7mm or .50 caliber) machine-guns. It will probably another year or so before ALON starts showing up in vehicles, so that more testing can be done to see if there are any unknown flaws in the material.