For marijuana smokers, glass is by far the most popular material of choice when it comes to their smoking implements. However, metal is also quite popular, and many pipes and bongs may contain one or more components made out of metal. In some smoking paraphernalia, plastic is used as well, although it is much less commonly used than metal and glass.
The choice of material is an important consideration for smokers, affecting not only the flavor and aroma of the smoke, but the chemical makeup as well. For instance, glass is a totally inert material that will not impart any unwanted flavors or odors into the smoke. More importantly, glass will not produce any toxins that can be harmful to the health. For purpose of safety and preservation of the original flavor of the weed, glass is by far the best choice of material.
Of course, other materials have their benefits as well. One of the most significant drawbacks of glass is its breakability, which is why many opt for more durable materials that will not break even when dropped. Metal is ideally suited for this reason, which makes it a popular choice of material for pipes as well. Metal is also strong and quite durable, so it will withstand repeated heating. It will also not break even with rigorous use, so a metal pipe will last a good long time.
There are quite a few drawbacks to metal, however. Metal conducts heat very efficiently, which makes it suitable for numerous applications, but less so for smoking purposes. A pipe made entirely out of metal would likely heat up too easily to be of practical use, although this disadvantage may be offset by lengthening the stem and mouthpiece.
But a more significant disadvantage of metal is the possibility that it could leach harmful toxins into the smoke. Most types of metal emit harmful compounds when heated, and smoking out of them may entail a serious health risk. Although some people get around this drawback by heating up the metal components thoroughly before use, there is still no guarantee that heating will remove all the harmful toxins in the metal.
Plastic is a much less commonly used material in smoking implements for obvious reasons. Nearly all plastics will melt when heat is applied, which obviously makes it unsuitable for use in pipe bowls. Even if heat resistant plastic is used, there is still a risk of harmful toxins ending up in the smoke.
That being said, plastic may be used in parts of the pipe that do not come into direct contact with heat. For bongs or hookahs where the mouthpiece is extended well away from the main chamber and the bowl, it may be possible to employ plastic both in the hose and in the mouthpiece. Of course, precautions will still have to be taken when using such implements. It will be necessary to use only laboratory grade plastics with no emissions for instance, and to avoid contact with heat at all times.