Buoyancy

1 unit of buoyancy counters 1 unit of lost Vertical Thrust. Neutral buoyancy occurs when your ship has a buoyancy 70 times its mass.

Buoyancy comes from balloons, cloudstone (armour plate or background) and blubber (blocks or background blocks, made using the Background Meat Block recipe). Balloons give large amounts of buoyancy, but are very fragile and can explode when damaged.