Ice
From Space Engineers Wiki
Ice, which can be processed in a Oxygen Generator to produce Oxygen, required to sustain the player. Oxygen can be pumped into sealed rooms using Air Vents or into a Medical Room, via the conveyor system. Oxygen is stored in Oxygen Tanks or Oxygen Bottles which are portable.
It is distinctive in its appearance, being mottled white and blueish in colour, with a "translucent" look to it.