"Bouncing" is an unofficial technique possible in most Balloon Fight games to date. It is usually used to quickly descend when Diving is not possible.
To "Bounce", simply fly all the way to the ceiling of the stage (Or to the bottom of a Platform) and fly into it at maximum speed to bounce downward and then stop flying so that you do not regain momentum upward. This is most useful when you are near the top of the stage and must descend to reach a Balloon, Balloon Bird, or a Giant Bubble. Bouncing can also be accomplished by touching a Flipper or a Bumper, though that is much less predictable. Bouncing has far greater effect with only one Balloon. While it is usually used to descend, it can be accomplished by bouncing off of the side of a Platform in order to bounce sideways.
Bouncing becomes an issue when the player is trying to use the ceiling or a Platform to Shield, because the player will bounce off of the platform they are trying to use as cover, possibly allowing enemies to pop your Balloons. The best way to avoid this is to simply either hold B to keep flying up if you have two Balloons left, but if you only have one, it is best to simply Hover under the platform, but close enough to be protected.