Quick answer
A dielectric fluid does not conduct electricity, so servers can be submerged in it. Single-phase immersion uses fluids that stay liquid (mineral oils, synthetic hydrocarbons such as PAOs, synthetic esters); two-phase immersion uses engineered fluids that boil at low temperature. Water-glycol coolants such as PG25 are not dielectric and must stay inside sealed loops.
Key takeaways
- Dielectric strength, viscosity, thermal properties and material compatibility decide suitability.
- Single-phase fluids are mostly hydrocarbons or esters; two-phase fluids are engineered, often fluorinated.
- Hardware makers qualify specific fluids; use their list.
General information. Confirm the exact fluid, equipment and qualification with your hardware or CDU supplier before specifying.
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Why immersion needs a dielectric
In immersion cooling, the fluid touches boards, connectors and power components directly. It must insulate electrically, carry heat away, and not attack plastics, seals or labels over years of contact. That is why immersion fluids are a different product category from the water-glycol coolants used in direct-to-chip loops.
Main types
| Type | Phase | Notes |
|---|---|---|
| Mineral oil | Single | Low cost; higher viscosity; long history in transformers. |
| Synthetic hydrocarbons (e.g. PAO, GTL-based) | Single | Consistent properties; widely used for single-phase immersion. |
| Synthetic and natural esters | Single | Higher biodegradability for some products; check compatibility. |
| Engineered fluorinated fluids (e.g. HFO-based) | Two-phase (some single) | Low boiling point; regulatory attention on PFAS. See Novec alternatives. |
Properties to compare
- Dielectric strength and volume resistivity.
- Viscosity across operating temperature (affects pumping and heat transfer).
- Thermal conductivity and specific heat.
- Flash point and fire classification.
- Material compatibility with server components, cables and tank seals.
- Boiling point (two-phase) and vapour management.
- Environmental and regulatory profile, including GWP and PFAS status.
- Hardware qualification and warranty position.
Who supplies them
See immersion cooling fluid suppliers and supplier profiles such as Shell, Engineered Fluids, Submer and Chemours.
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Get the checklist →Frequently asked questions
Is PG25 a dielectric fluid?
No. Water-glycol coolants conduct electricity and are only used inside sealed cold-plate loops.
What fluid is used for single-phase immersion cooling?
Typically mineral oils, synthetic hydrocarbons or esters that remain liquid in operation.
What fluid is used for two-phase immersion cooling?
Engineered fluids with a low boiling point; historically 3M Novec products, now alternatives such as Chemours Opteon 2P50.
How we source this page
- Facts come from manufacturer pages, datasheets, owner's manuals and standards bodies, linked under Sources.
- We do not test products, and no brand pays to be listed or ranked. Advertising and affiliate links are labelled and never change the data.
- Anything we could not find is marked "not published" rather than guessed. Spotted an error? Tell us.