Glass is the ultimate smoking utensil. When it comes to purchasing a glass water pipe or bong, there are a few very important factors to consider. High-quality pieces are blown by reputable brands using only borosilicate glass. Avoid the cheap knock-offs on the market because they are made from low-grade chinese glass by less-than-talented workers.A frosted glass-on-glass joint (where the bowl slides into the downstem) is a necessary component for unsurpassed air-tightness and taste.Glass thickness plays a critical role in the life expectancy of a bong. The most common thicknesses are 5mm, 7mm, and 9mm, with the thickest obviously being the most durable and long-lasting.The entire point of utilizing a bong is to filter and cool the smoke before it enters one's lungs. When the smoke must bubble through many tiny holes before reaching the user, the contact area between smoke and water is increased, creating a smoother hit. This is called diffusion. An immense variety of methods are available to achieve this, including percolators, ash catchers, and diffused downstems.Finally, a bong should be visually appealing to its owner. Because every glassblower has their own style, each water pipe is a unique piece of art that is meant to be cherished for as long as possible.Of course there are many other factors at play such as size and shape, not to mention all the other possible variations, but in the end it all comes down to personal preference and making a decision that you will enjoy.