An open cell sealing product is one whose cells are not totally enclosed by its walls and are open to the surface either directly, or by interconnecting with other cells.
In a closed cell product, cells are entirely enclosed by its walls and not interconnecting with other cells.
A material’s sealing effectiveness should be based on performance, not just on its open or closed cell structure. This is why it’s important to consult with a materials expert (such as our on-staff pros!) when specifying a sealing product.
Not all cellular materials are comprised of 100% open or 100% closed cells. It’s common to have a blend of open and closed cells. Understanding the advantages and disadvantages of each is important.
Open cell materials typically resist compression set and force relaxation better than closed cell materials, but are not as effective at resisting water absorption in an uncompressed state. However – at a certain level of compression – the small openings in the cell walls of an open cell foam will “close off,” resulting in an effective seal.
Open cells in an uncompressed state can be infiltrated by liquids and gases; not necessarily a bad thing since they usually release that absorbed air or moisture over time. Common applications for open-cell materials include thermal insulation, filters, acoustic absorption, shock and vibration management and cushioning.
Closed cells in an uncompressed state contain pockets of gas enclosed in an elastomeric “shell.”
Common applications for closed cell materials include floats requiring good buoyancy and water resistant crafts.
When it comes to liquid or gas absorption, cell structure plays an important role. The cell voids in an open cell material can vary significantly. Open cell foams can be reticulated, meaning there are more open voids than wall structures, giving the appearance of cell striations. Even under compression, the reticulated structure will not “close off” unless compressed to a solid mass. PORON Urethane and BISCO Silicone cell voids will “close off” at lower levels of compression, resulting in a seal while the material is still in a fairly low range of compression force deflection.
Choosing the right cell structure requires some homework. Luckily, our materials experts are here to help you every step of the way.