Compression set is the part of a seal's squeeze it never recovers after being compressed for a long time, expressed as a percentage – the lower the better. A seal with high compression set goes flat and stops sealing. It rises with heat and time, and depends mostly on the material: EPDM and silicone recover well, PVC and some foams less so.
How it is tested
A sample is squeezed by a fixed amount (often 25%) and held at a set temperature for a set time, e.g. 22 or 70 hours. After release, the lost height is measured as a percentage of the squeeze. Always compare results tested under the same conditions.
Material comparison
| Material | Typical compression set (general grades) |
|---|---|
| EPDM (solid / sponge) | Low to medium – good recovery |
| Silicone | Low – good, even at high temperature |
| TPE / TPV | Medium – higher at heat |
| PVC | Medium to high |
| PU foam | Good when new, rises with ageing |
Design tips
- Do not over-compress: 20–40% squeeze is a common target for hollow and sponge seals.
- Use a hollow (D or bulb) section rather than solid where closing force should stay low.
- For heat, choose silicone or a heat-resistant EPDM compound.
Need a seal for this?
Send your section, gap size or a photo of the old seal – Dora replies usually within 2 hours. Custom extruded & moulded rubber parts are available from 10 m.