Why does wet helium balloons fall?

Answer 1

Helium filled balloons eventually fall because the helium molecules escape from the envelope of the balloon, both at the neck of the balloon and through the material of the balloon itself. The same occurs with air-filled balloons but air-filled balloons do not float to begin with -- they fall to the ground no matter how much air you put in them. In order to float, the gas within the balloon must be lighter (less dense) than the gas outwith the balloon. Inflating a balloon with the same density of gas that surrounds it will not make it float upward because the weight of the balloon alone will make it fall under gravity. Moreover, the elasticity of the balloon compresses the gas within, making it much denser, and therefore heavier.

Answer 2

The balloons initially rise because helium is far less dense than almost any other gas. They begin to fall because helium is very small, and simply passes straight through the balloon, until the total density is not enough to make it rise or remain up.

Answer 3

Wet helium balloons fall because the water adds weight to the balloon, causing it to lose its buoyancy and no longer float. The added weight of the water changes the overall density of the balloon, making it heavier than the surrounding air and causing it to descend.

Answer 4

The water on the balloon's surface adds extra weight and causes it to fall. As the water drips off/evaporates, the balloon will slowly rise back to its original position.