Air

Please excuse the lack of photo. Air is a thickener we commonly take for granted, but bubbles slow the flow of water as well as any other type of thickener. Where would our egg white foams be without it? Of course the trouble with bubble thickening is that bubbles tend to pop. That’s largely a result of gravity which draws liquid down the sides of the bubble walls until they become so thin that they burst. The problem can be mitigated with the addition of various substances that reinforce bubbles walls: sugars, fats, proteins or starches.