Balloons were a type of aircraft supported in air by buoyancy, which in effect, made the airship lighter than air.
In 2268, Doctor Leonard McCoy compared the sudden onset of weakness in the crew of the USS Enterprise to a balloon popping. (TOS: "The Immunity Syndrome")
According to a diagram drawn by Robert H. Goddard, the height limit for a balloon (on Earth) was twenty miles. (Star Trek: Enterprise opening credits)
A painting in Marla Aster's quarters aboard the USS Enterprise-D in 2366 depicted a balloon craft descending in the atmosphere of Jupiter. (TNG: "The Bonding")
In 2367, while playing in the arcade on Ogus II, Jake Potts popped a balloon filled with red pillion dye to scare his brother Willie into thinking he'd killed him. (TNG: "Brothers")
In the holographic program titled Julian Bashir, Secret Agent, Hippocrates Noah described his plan cause the surface of the Earth to shrink as being "just like letting air out of a balloon." (DS9: "Our Man Bashir")
Types of balloons