Who makes single-phase dielectric for AI data centers

A single-phase dielectric fluid does two things ordinary coolant cannot: it does not conduct electricity, so live hardware can sit in it, and it stays liquid throughout the loop, so the system is a pump-and-heat-exchanger problem rather than a pressure vessel. That combination is what open-bath immersion is built on — a tank of fluid, boards submerged in it, heat carried out to a water loop through an exchanger. The fluids themselves are mostly hydrocarbon or ester based: synthetic oils, mineral oils, and increasingly bio-derived esters. They are cheap relative to fluorinated alternatives and face far less regulatory pressure, which is the main reason single-phase immersion has kept moving while two-phase has not. The costs are practical ones: viscosity affects pumping power, fluid interacts with plastics, labels, thermal interface material and cable jackets over time, and servicing hardware means pulling it dripping out of a tank. AI is an awkward fit for this part, which is worth saying plainly. Immersion handles high rack density well, but the accelerator vendors' reference designs have converged on direct-to-chip cold plates, and a fluid choice that is not on a vendor's supported list is a warranty conversation. What to look for is material compatibility data and whether a fluid has been qualified by a hardware maker rather than only by the tank vendor.