When a customer needs a gasket that will not take a permanent set after being compressed for months or years, the conversation almost always comes down to two materials: PORON urethane foam and silicone foam. Both are excellent, but they have different strengths. The PORON compression set vs silicone compression set comparison is something I walk through regularly, and the right answer depends on your application. Let me break it down.
Why compression set resistance matters for gasket materials
Quick recap: compression set is the permanent deformation a material retains after being compressed and then released. If a gasket takes a high compression set, it does not spring back to its original thickness, which means it loses sealing pressure over time. A low compression set material maintains its thickness and sealing force even after extended compression. This is critical for enclosure gaskets that are bolted down and left alone for years. The lower the compression set percentage, the better the material maintains its seal over the service life of the product.
PORON urethane foam compression set performance
PORON urethane foam from Rogers Corporation is one of the best open cell materials for compression set resistance. PORON compression set performance is exceptional: the PORON 4701 series, from 4701-30 through 4701-60, typically shows compression set values under 10% when tested per ASTM D3574. That is exceptional for a foam material. The reason PORON excels is its microcellular urethane chemistry combined with a very fine, uniform cell structure. The material is designed specifically to withstand repeated compression cycling without losing thickness. We cut a lot of PORON urethane foam for electronics enclosures where the gasket is compressed and released repeatedly, and the low compression set is what keeps the seal intact over thousands of cycles. PORON also comes in multiple densities, so you can pick the firmness that matches your closure force. The 4701-30 is the softest grade, and the 4701-60 is the firmest in that series.
Silicone foam compression set performance
Silicone foam is the other heavyweight in this category. Silicone compression set performance is even better than PORON in many cases: grades like HT-800, HT-820, HT-840, and HT-870 from Saint Gobain typically show compression set values under 5% per ASTM D1056 testing. The Saint Gobain R10480S, R10480M, and R10480F12 silicone foam grades also come in under 5%. The reason silicone foam excels is the inherent resilience of the silicone polymer backbone. Silicone has excellent elastic recovery, and the foam structure preserves that property. The bonus with silicone foam is temperature resistance: it handles both low temperatures and high temperatures far better than PORON. If your gasket needs to maintain low compression set across a wide temperature range, silicone foam has the edge. The HT-800 silicone foam grade is a proven performer we cut frequently, and it is one of the most popular silicone foam grades for enclosure gasketing where long-term sealing reliability is critical.
PORON vs silicone foam: head to head comparison
|
Property |
PORON urethane foam |
Silicone foam |
|---|---|---|
|
Compression set |
<10% per ASTM D3574 |
<5% per ASTM D1056 |
|
Temperature range |
-20F to +250F |
-80F to +500F |
|
Softness |
Very soft, multiple densities |
Very soft, multiple densities |
|
Water resistance |
Open cell, not waterproof |
Varies by grade, partially open cell |
|
Compression cycling |
Excellent for repeated cycling |
Excellent for static compression |
|
Cost |
Moderate |
Higher than PORON |
|
Availability |
Wide range of thicknesses and densities |
Good range, some lead times on specialty grades |
Both materials are soft gasket options that we cut regularly. PORON wins on cost and repeated compression cycling. Silicone foam wins on compression set values and temperature range. For more on how silicone foam compares to closed cell sponge, see our silicone sponge gaskets page. One thing to keep in mind: neither of these materials is a good water seal. Both are open or partially open cell, so if waterproofing is a requirement, you may need to pair them with a closed cell gasket or choose a different material entirely.
Choosing the right low compression set material
Here is how I help customers decide:
- Temperature exposure: if the gasket sees temperatures above 250F or below -20F, silicone foam is the clear choice. PORON is limited to moderate temperatures.
- Cycling frequency: if the gasket is compressed and released repeatedly, like a door or access panel, PORON handles dynamic cycling very well. Its microcellular structure is built for it.
- Fluid exposure: neither is ideal since both are open or partially open cell, but silicone foam has better chemical resistance than PORON. For damp environments, fungus resistant gaskets may be needed.
- Compression percentage: both handle 25-50% compression well. PORON is more forgiving at higher compression levels.
- Enclosure design: for lightweight plastic enclosures with low closure force, PORON in very soft grades like 4701-30 is a great fit. For high-temperature enclosures, silicone foam is the proven choice.
- Budget: PORON is generally less expensive than silicone foam, which matters for high-volume production runs.
More information on low compression set gaskets
If you need a gasket material with low compression set, we stock and die-cut both PORON urethane foam and silicone foam in a range of densities and thicknesses. We can provide technical data sheets, material samples, and custom-cut prototypes for testing. Whether you need a few prototypes or production volumes, we can help. For questions or quotes, contact sales@nedc.com.
FAQ
What is the compression set of PORON?
PORON urethane foam, including the 4701-30 through 4701-60 grades, typically shows compression set values under 10% when tested per ASTM D3574. This low compression set is due to the microcellular urethane chemistry and fine cell structure that resists permanent deformation even after repeated compression cycling.
What is the compression set of silicone foam?
Silicone foam grades such as HT-800, HT-820, HT-840, and HT-870 typically show compression set values under 5% per ASTM D1056 testing. Saint Gobain R10480S, R10480M, and R10480F12 grades also test below 5%. The excellent elastic recovery of the silicone polymer gives silicone foam its superior compression set performance.
Which has better compression set: PORON or silicone?
Silicone foam generally has better compression set values (under 5%) compared to PORON urethane foam (under 10%). However, PORON excels in applications with repeated compression cycling due to its microcellular structure, and it is more cost-effective. The best choice depends on temperature range, cycling frequency, and budget.
What is a low compression set material?
A low compression set material is a gasket material that retains most of its original thickness and sealing force after being compressed for an extended period. Materials with compression set values below 10-15% are generally considered low compression set. These materials resist permanent deformation and maintain effective seals over long service lives. Both PORON urethane foam and silicone foam qualify as low compression set materials.