Material Compatibility in Immersion-Cooled Servers
In immersion cooling, the fluid touches every material in the server for years. A component checklist and the test procedure described by OCP.
Updated 9 November 2026 · Published by IsoTec
Why compatibility decides success
Compatibility works in two directions. The fluid can attack materials: elastomers swell or shrink, plastics soften or become brittle, adhesives let go. And materials can contaminate the fluid: plasticisers, dyes, adhesive components or flux residues dissolve, change the colour and can lower resistivity and dielectric strength. Both effects build up slowly and are often noticed only after months.
Component checklist
| Component | Typical risk | What helps |
|---|---|---|
| Cable assemblies with PVC sheaths | Plasticisers leach out; sheath becomes stiff, brittle and cracks; fluid is contaminated | Sheaths of PUR or fluoropolymers; test the actual cables |
| Thermal paste and greases (TIM) | Grease matrix dissolves or washes out; chip temperature rises | Solid TIMs such as graphite pads or indium foil |
| Seals, gaskets, EMI foams | Swelling or shrinkage, loss of sealing | FKM or PTFE often robust; EPDM, natural rubber and some silicone and NBR grades tend to swell – test |
| Electrolytic capacitors, coin cells | Swelling of seals | Check seal material with the component maker |
| Labels, tapes, adhesives, inks | Labels peel off and sink; inks dissolve | Immersion-rated labels, acrylate adhesives, laser marking |
| Optical transceivers and fibres | Fluid in the optical path, signal loss | Immersion-qualified optics |
| Connectors, sockets, plastic parts | Dimensional change, contact resistance | Low-level contact resistance tests after soak |
| Conformal coatings, flux residues | Dissolution, fluid contamination | Clean assemblies; test coated boards |
| Hard disk drives | Non-sealed drives fail | SSDs or hermetically sealed drives |
| Fans | Drag in the fluid, wasted power | Remove or switch off |
What is different with esters?
Esters are more polar than hydrocarbons. This gives them good solvency and high moisture tolerance, but it also means they can extract plasticisers and interact with some plastics and elastomers differently from hydrocarbons. Fluoroelastomers (FKM) and PTFE generally perform well; for nitrile rubber (NBR) the result depends on the grade. Results from hydrocarbon fluids cannot simply be transferred to esters – the test has to be done with the actual fluid.
How compatibility is tested
The OCP guideline Server Component Immersion Material Compatibility Testing (v1.5, June 2026) describes the procedure for single-phase fluids:
- Heat soak at 80 °C ± 2 °C for 14 days in a closed vessel, sample fully immersed, at least about 0.8 L of fluid
- Several replicates to show the spread of results
- Material checks: visual inspection with photos, change in mass, volume, dimensions and hardness (Shore), functional tests such as contact resistance, dielectric withstand voltage, signal integrity and optical performance
- Fluid checks: appearance, colour, turbidity and sediment before and after; screening for contaminants such as plasticisers, metal ions, water and organic acids
- Pass/fail: the fluid must still meet the OCP Immersion Requirements after the soak
The guideline sets no acceptance limits and does not predict service life. Longer tests and a trial in a real tank add certainty.
Practical tips
- Test the exact part numbers of the bill of materials – the same component from two suppliers can behave differently.
- Run a blank sample of the fluid without components as reference.
- Include worst-case parts: cables, labels, gaskets and thermal materials.
- Re-test when the hardware generation or the fluid changes.
Compatibility testing at IsoTec
We soak your components in our ester fluids, document the changes to the materials and analyse the fluid before and after. You receive a test report as a basis for your qualification. See the qualification checklist and the data center immersion cooling guide.
Frequently asked questions
Can PVC cables be used in immersion cooling?
Often not long-term: plasticisers can leach out of PVC sheaths, which makes them brittle and contaminates the fluid. PUR or fluoropolymer sheaths are commonly used instead. Test the specific cable.
Does thermal paste work in immersion cooling?
Many greases wash out over time. Solid thermal interface materials such as graphite pads or indium foil are used instead.
How long does a compatibility test take?
The OCP guideline describes a 14-day soak at 80 °C for single-phase fluids, plus time for measurements before and after.
Related articles
- Immersion Cooling Fluids for Data Centers
- How to Qualify an Immersion Cooling Fluid
- OCP Immersion Fluid Requirements Explained
- Immersion Cooling Fluids Compared
Sources and further reading
Test your components in our ester fluids
Send us your bill of materials and samples – we run the soak tests and report the results. IsoTec products are supplied to customers outside Germany.