It is well known that water filtration is effective at cooling smoke, but it also filters the smoke. There are several issues of note when considering the effectiveness of filtration. The bubble is a smoke-water membrane in the context of bong diffusion. This membrane is where filtration happens. This filtration is the exact reason bong water turns yellow and starts to stink even if ash never gets in it: materials are passing from the smoke into the water via the surface of the bubble. Smaller, more numerous bubbles means more surface area, consider the greater surface area of 6 12 ounces as opposed to 1 2-liter (not exactly equal quantities, but close enough to be illustrative). More surface area means more area for smoke and water to interact, allowing particles in the smoke to pass into the water. Due to the low affinity between water and THC most of the material that passes into the water will be undesirable content and not drug matter. The benefit of surface area is that provided by diffusers, i.e. devices that break the bubbles into smaller bubbles such as slits or gridding. The second way to get more interaction between the smoke and water at the bubble median is simple duration of contact. This is facilitated by two things: percolators (multiple chambers) and stacking, which is the phenomenon whereby a column of bubbles is achieved keeping the bubbles intact and alive longer to transfer tar between the smoke and the water. Excess filtration can adversely affect taste by removing flavorful constituents but generally will benefit smoothness across the board.