Compression set with gaskets is a constant concern because it eventually creates sealing issues with the interface of the gasket and the surface it is being pressured against. Compression set is a concern because the gasket will lose thickness and lose its ability to fill the gap. It is not always evident immediately that thickness is being lost as temperature cycling goes on with a gasket.
Definition of Compression Set
Compression set is defined as what percentage of the original height of the material does the material return to after it has been subject to compression in a certain environment. For example, an .125’’ piece of gasketing material is compressed 50% to .063’’. After removal of the fixture, it stays at .099’’. That would be a compression set of 42%.
Zero Percent Compression Set would be the material returned to its original height.
One Hundred Percent Compression Set would be the material stayed at whatever percentage it was compressed to.
When testing for a compression set, the lower the number, the better. In the gasket industry, a compression set of below 25% is pretty good. However, there are some gasketing materials that standard apart from that. Anything below 10% I would consider excellent compression set resistance. This is what this blog is about.
The Standards/Requirements for Compression Set
There are three highly used standards for testing materials for compression set:
Solid Rubber Compression Set Standards
ASTM D395 is the recognized authority on compression set for harder gasketing material that is commonly rubber.
Sponge/Foam Compression Set Standards
There are two specifications that are used often in the foam/sponge testing arena. ASTM D1056, and ASTM D3574 are the most commonly used. These are the recognized authorities for compression set for softer materials such as foam/sponge rubber materials.
Materials Used
Silicone rubber products, and Urethane Foam are some of the most notorious for their low compression set values. In the charts below we demonstrate some of those values.
Sponge/Foam Rubber Gasket Materials Low Compression Set
| Product | Compression Set % Max | Requirement stated per their datasheet | Type of Product |
| Rogers Corporation HT-800, HT-820, HT-840, HT-870 | <5% | 22 hours @ 212°F ASTM D1056 | Silicone Foam |
| Saint Gobain R10480S | <5% | 22 hours @ 212°F ASTM D1056 | Silicone Sponge |
| Saint Gobain R10480M | <5% | 22 hours @ 212°F ASTM D1056 | Silicone Sponge |
| Saint Gobain F12 | <5% | 22 hours @ 212°F ASTM D1056 | Silicone Foam |
| Poron® 4701-30 | <10% | ASTM D3574 Test D 158°F | Urethane Foam |
| Poron® 4701-40 | <10% | ASTM D3574 Test D 158°F | Urethane Foam |
| Poron® 4701-50 | <10% | ASTM D3574 Test D 158°F | Urethane Foam |
| Poron® 4701-60 | <10% | ASTM D3574 Test D 158°F | Urethane Foam |
Solid Rubber Gasket Materials Low Compression Set
| Product | Compression Set % Max | Requirement stated per their datasheet | Type of Product |
| Saint Gobain Norseal 9030 | 15% | 70 hours @ 302°F ASTM D395 Method B | Silicone Rubber |
| Saint Gobain Norseal 9040 | 15% | 70 hours @ 302°F ASTM D395 Method B | Silicone Rubber |
| Saint Gobain Norseal 9050 | 15% | 70 hours @ 302°F ASTM D395 Method B | Silicone Rubber |
| Saint Gobain Norseal 9060 | 20% | 70 hours @ 302°F ASTM D395 Method B | Silicone Rubber |
| Saint Gobain Norseal 9070 | 20% | 70 hours @ 302°F ASTM D395 Method B | Silicone Rubber |
For more information on low compression set gaskets, please contact sales@nedc.com.