What is an open cell gasket?
An open cell gasket is made from foam where the individual cell walls are broken or incomplete, so the cells interconnect like a sponge. Air and fluids can pass through the structure. This gives open cell foams their characteristic softness and conformability. When you compress an open cell gasket, the material squishes and fills gaps, but it does not block fluid passage because the cells are connected. Under ASTM D1056 classifications, open cell foams are typed differently from closed cell, with designations accounting for compression deflection and density. Open cell foams generally have lower density and lower compression resistance than their closed cell counterparts.
What is a closed cell gasket?
A closed cell gasket is made from foam where each cell is a discrete, sealed bubble. The intact cell walls trap gas inside, giving the material internal pressure rating and structural integrity. Because the cells are sealed, closed cell foams resist water absorption and provide a barrier against moisture, air, and dust. Closed cell gaskets are the go-to for a waterproof gasket. They are denser and firmer than open cell foams, and recover their shape well after compression.
Softness: open cell vs closed cell foam gaskets
In most cases, an open cell gasket is softer than a closed cell gasket of similar density. When you press on an open cell foam, air escapes through the interconnected cells and the material compresses easily. With closed cell foam, trapped air inside each sealed cell resists compression, so the material feels firmer. This shows up in compression force deflection (CFD) values: open cell foams typically have lower CFD, meaning less force needed to compress them. For delicate enclosures or lightweight plastic housings, a soft foam gasket with an open cell structure is often the better fit.
Sealing performance: water, air, and dust
Closed cell gaskets excel at sealing against water because sealed cells do not let moisture pass through. If your enclosure needs to survive rain, washdown, or submersion, closed cell is the way to go. Open cell gaskets are generally not good water seals because water can wick through the interconnected cells. But open cell foams are excellent at dust and air sealing. The soft, conformable nature of open cell foam fills uneven surfaces and creates a good seal against particulate matter. For environmental gasketing where dust and air are the concern rather than water, open cell works well.
Material options for each cell structure
The material you choose often dictates the cell structure:
- Silicone sponge: closed cell. A popular silicone sponge gasket material with excellent water resistance and compression recovery.
- Silicone foam: can be open or partially open cell. The silicone foam vs silicone sponge comparison is worth reading if you are deciding. Silicone foam gaskets tend to be softer and lower density than sponge.
- PORON urethane: open cell microcellular. PORON urethane foam offers outstanding compression set resistance with a very fine cell structure.
- Crushed EPDM: mostly open cell. The crushing process breaks cell walls for a softer, more conformable material.
- Neoprene and EPDM sponge: typically closed cell. Standard commercial sponge materials for weatherstripping and enclosure sealing.
When to choose open cell vs closed cell
Here is my decision framework:
- Water sealing: go closed cell. If water ingress is a concern, open cell will not work.
- Dust sealing: open cell excels due to conformability, though closed cell also performs if compression is adequate.
- Low compression pressure: open cell is generally softer, ideal for lightweight enclosures.
- Softness: for extremely soft gaskets, open cell materials like PORON or silicone foam are usually best.
- Compression set: both structures can offer good recovery, but low compression set gasketing often comes down to material chemistry rather than cell structure alone.
For more on this, see our page on open cell foam and sponge materials.
More information on soft foam gaskets
If you need help selecting the right cell structure, we stock and die-cut a wide range of open cell and closed cell materials. We can provide samples, data sheets, and custom-cut prototypes. For questions or quotes, contact sales@nedc.com.
FAQ
What is the difference between open cell and closed cell gaskets?
Open cell gaskets have interconnected cells that allow air and fluids to pass through, making them softer but not waterproof. Closed cell gaskets have sealed cells that resist water absorption, but are firmer.
Are open cell gaskets softer than closed cell?
Yes, in most cases. The open cell structure allows air to escape during compression, reducing force needed. Closed cell foams trap air inside sealed cells, creating internal resistance that makes the material firmer.
Can open cell gaskets seal against water?
No. The interconnected cell structure allows water to wick through the material. For waterproof sealing, closed cell gaskets like silicone sponge, closed cell neoprene, or closed cell EPDM are the right choice.
Which is better for dust sealing: open or closed cell?
Both can work, but open cell gaskets often have an edge due to superior conformability. The soft, compressible nature of open cell foam fills uneven surfaces and gaps, creating an effective dust barrier.