Rubber parts that sit in oil, fuel or hydraulic fluid can swell, soften or shrink. ASTM D471 is the standard way to measure how much. Here is what the test does and how to use the results.
What ASTM D471 tests
ASTM D471 covers the effect of liquids on rubber. Test pieces are weighed and measured, then immersed in a chosen liquid for a set time at a set temperature. After immersion they are measured again.
- Volume change. How much the rubber swelled or shrank, as a percentage.
- Mass change. How much liquid the rubber absorbed.
- Property change. How hardness, tensile strength and elongation changed compared with unaged samples.
How to read the results
A small volume change usually means the rubber is compatible with the liquid. Large swell is a warning: seals can extrude, jam or lose their grip. Large shrinkage can open a leak path after the liquid dries out or is extracted. The test conditions should match the real service: same liquid, same temperature, same time.
Why it matters when choosing a compound
- Different rubbers react very differently to the same oil. A compound that works in water may fail in fuel.
- Test data on your own liquid is better than a general compatibility chart.
- Hardness and strength after immersion tell you whether the part will still work, not just whether it survived.
Common mistakes
- Testing in a similar liquid instead of the real one. Oils and fuels vary a lot between brands and grades.
- Checking only volume change and ignoring hardness and strength after immersion.
- Using room-temperature data for a part that runs hot. Heat speeds up swelling and breakdown.
- Forgetting the cleaning fluids and coolants the part also sees.
Each of these can make a compound look fine on paper and fail in the field. A short test plan written up front is cheap compared to a field return.
What to put on your drawing
If a part will see oil, fuel or another fluid, list the fluid, the temperature, the immersion time and the maximum allowed volume change and property change. Cite ASTM D471 as the test method. That gives your supplier a clear target. This is an overview, not a replacement for the standard itself.
See our full ASTM D471 page, compare materials in material technology, and watch more in the Rubber Testing Video Library.
Have a part that needs to hold its shape or pass a spec? Send the drawing or sample requirements to estimator@coirubber.com and our engineering team will review it. Coi Rubber has been in business since 2003, is US owned and operated, and our Wuhu, China manufacturing facility is IATF 16949 certified.