According to the physics, the answer is clear: air is a wonderful insulator, and so a thick layer of air trapped inside soap should keep more heat in the tub for longer. Most of the heat lost during a bath isn’t through the interaction between water surface and air, but through the walls of the tub (cast iron tubs suffer especially). One of the scientists even confirmed the assertion with an experiment. Filling two identical bowls with an identical amount of water, he measured the temperature over time for each, one covered with a layer of bubbles, one without suds. The water with the layer of bubbles lost less heat over time, almost 50 percent less. And because this small scale result should scale up, that means a bubble bath should stay hotter, longer.
found @ 19600 likes ON 2019-01-01 05:03:15 BY ME.ME