The mechanics of a bong are compared to those of a laboratory gas washing bottle. Bongs are often either glass or plastic that use a bowl, stem, and water to produce smoke. After the bowl has been packed and water has been inserted into the bong, the substance is lit and the smoke is drawn through water to produce a smoother smoke than other methods of smoking do. To smoke a bong, the smoker must inhale in the bong so bubbles containing smoke begin to come from the stem. Once the bong has a fair amount of smoke built up, the stem is separated from the bong and the remaining smoke will go into the smoker's lungs.