perfluorocarbons.

[spike4597]

in real life, there is a material called a perfluorocarbon. it is a breathable liquid. that is to say, you can inhale it and breath it just like air. maybe add a "breathable liquid" that can be used for underwater bases, allowing dupes to breath underwater. or maybe, since it is denser than oxygen, it can be used to make long-term suits that have smaller penalty.

[DazyCat]

It's breathable because oxygen can dissolve in it at a good amount. Maybe add a machine to bubble oxygen through this liquid to make saturated O2 solution for dupes to breathe in. As they breathe, oxygen will be gradually depleted and the liquid needs to be periodically refilled with O2 to continue usage. A fully saturated fresh solution can be light bule, and a depleted solution can be gray to indicate oxygen concentration. This would be very helpful with the water asteroid because you can't make a room filled with oxygen underwater because the water pressure will push all gas into a square. Imagine filling a room underwater with this liquid that won't be compressed so dupes can take a underwater breath break and refill their suits without needing to go all the way above water.  

[meekay]

I'm currently trying to mine out the superconducting asteroid and would love to get a suit that works submerged in magma.
Maybe some extra downsides if you soil your suit though.