Why do bubbles pop?
Bubbles pop when their thin film of soapy water breaks. The film thins as water drains down and evaporates, and a touch from dust, a dry surface or a pinprick can rupture it.
A soap bubble is a thin layer of water trapped between two layers of soap molecules, surrounding a pocket of air. Surface tension pulls the film into a sphere, the shape with the smallest surface area for the air inside. The soap stabilizes the film, making it stretchy enough to hold its shape.
Over time, gravity pulls water down to the bottom of the bubble, making the top thinner. Water also evaporates into the air. When part of the film becomes only a few millionths of a centimeter thick, it can break. The hole spreads around the bubble in a fraction of a second.
Making longer-lasting bubbles
Adding glycerin or sugar to bubble solution slows evaporation, helping bubbles last longer. Humid days are better for blowing bubbles than dry ones. Touching a bubble with a wet finger often does not pop it, while a dry finger usually does.
Did You Know?
The swirling rainbow colors on soap bubbles come from light reflecting off the inner and outer surfaces of the thin film and interfering.