Supercritical CO2 is heavy like a liquid, with weird and useful properties
It's amazing how wide the applications of supercitical CO2 can be -- we used it as a solvent to extract high-value lipids from algal biomass at a biofuel company I worked for:https://en.wikipedia.org/wiki/Supercritical_fluid_extractionBut it can also be used as a 'solvent' in non-toxic and low/no-water laundry systems:http://e3tnw.org/ItemDetail.aspx?id=512In addition to all of the benefits it can provide for energy-related pursuits as a working fluid.