When we think about glass we think of something that is quite fragile and becomes damaged easily so it’s no wonder that the idea of a pipe or bong made of glass might raise questions with people. When you think of some of the most fragile items in your house it doesn’t seem like a good idea to stick those items into your mouth and add fire. The truth is however that glass is very good at handling the heat so long as that heat is applied in small amounts or at least applied evenly.
Glass needs to be heated up to 2,200 degrees to soften enough to work it into new shapes. At those temperatures, aluminum, copper, silver, gold and iron are already liquid and steel is starting to soften as well. Glass can handle the heat. No matter what you are smoking in it, it can handle the heat as long as you are just using your lighter to heat it up. Glass has two weaknesses that stem from its brittle nature. The first is heating the item to rapidly or unevenly can cause it to crack. The second is internal pressure. If you try using a bong or other device that doesn’t have a way to vent you can expect it to come apart. The temperatures needed to cause either one of these to happen are so high that they would cause you bodily harm to have near your face, to begin with. Heating up glass fast enough to compromise its tensile strength requires a heat source much larger than is available from a normal pocket lighter. The glass will dissipate heat on its own fast enough that you are likely to burn your lips long before you risk breaking your pipe from heat only.
So while glass is indeed fragile to physical forces making it easy to break, it is quite safe to exposed to heat. It also will not rust or corrode. Since glass does not rust, corrode, or take damage from heat or chemicals it won’t have surfaces that will hold harmful contents. So when you want something you can heat up, cool down, expose to chemicals, burn materials and chemicals in such as tobacco and flavored tobacco and yet still put in your mouth there are few materials that are safe and will remain safe over the life of the bong in question. Glass has been historically chosen for pipes for good reasons. Even if the science was not fully understood in the past it still remains that pipes have been made for glass for almost all of the five thousand years glassworking has been around, yet remain so common today. The decorative potential certainly helps imagine.