Researchers at Tokyo Metropolitan University have uncovered the real reason liquid drains from foams, resolving a long-standing scientific puzzle. Traditional physics models have consistently overestimated how tall a foam must be before liquid begins to leak out. By closely observing foam behavior, the team found that the key factor is not simply liquid moving through a fixed structure, but the pressure needed to rearrange the bubbles themselves. This finding emphasizes how important dynamic processes are when studying soft materials.

Anyone who has sprayed foam on a surface has likely noticed droplets forming and dripping from the bottom. This happens because foam is made up of tightly packed bubbles separated by thin liquid films, creating a complex network of pathways. Liquid can move through these pathways, either draining out or being absorbed into the foam when it comes into contact with it.…