Steam, as it is floating upward.

Steam was added in the chapter: Boiling Point

Steam is the only substance so far that floats upwards. Steam is generated when either Water or Poison Water touches Hot Rocks or when spewed from a pipe. Steam can be converted back into water by Icicles.

Steam is the substance that fills Allie Ducks with 5 drops and runs her Steam Powered Organ with 20 drops.

Steam can be contained in Balloons, and when the Steam balloon is filled, the balloon will float upwards. Balloons filled with Steam have a wispy, smoky design on them. Steam can float through Algae.

In Where's my Perry, steam lasers turn water to steam. When Steam interacts with Mud, the mud stays in its wettest form. It also, like Allie’s organ, can power up to tube to send Perry or any other Owca agent down to hq.