A simple toy that makes non-player entities float and stand still. According to Vaygrim, with Open Blocks Fans this can make to some funny ideas such as a villager carousel, or make a more silent cow farm for milking and such.
However, for player entities its different as it gives them an ability to "float" and feather-fall when jumping.
The balloon comes in the 16 minecraft colors. Should a balloon be attached to the player the player can simply pop it by looking up and hitting the balloon. If the Balloon is allowed to float up it will pop at world height (y:256).
It is useless when held in the player's hand, so it has to be placed on players and entities and blocks for the balloon's effect to work