When selecting a foam for your application, have you every wondered if open or closed-cell foams are better? At Marian, we recommend materials based on a product’s application. This is certainly true when it comes to foam materials for use as a gasket. This means in order to recommend the best material, our first step is to understand the conditions, forces, stress and other requirements the gasket will experience in your end product.
Material Options for Foam Gaskets and Seals
A common misconception is that open cell materials are an inferior material for use in static gaskets and seals. To be considered open cell, more than 50% of its cells must be open. It's true that in an uncompressed state, open cell foam (even micro-cellular) will allow some level of ingress. Because of this, you wouldn't want to use an open cell foam in a life vest. As a gasket and when sufficiently compressed, micro-cellular open cell urethane foam can form a more effective seal for a longer service life than many closed-cell foams.
Closed cell foams are a cluster of independent bubbles with gas trapped inside each cell. Open cell foam is composed of interconnected cells in a web-like fashion that has some amount of openness within each cell connected to the next cell in the web. When these openings are very small in a dense (heavy) foam, it is called micro-cellular open-cell.
Most closed cell foam materials have some open cells within their matrix. These may be cells that did not fully form during the blowing process. Typically a foam should have more than 70% closed cells before it can be labeled as such.
Under constant compression, a closed cell foam may lose compression force due to permeation of the gas enclosed in the cells or due to cell rupture from pressure. Under the same conditions, the micro-cellular open cell structure is able to maintain compression force because the cell structure is an interconnected web and not dependent on the gas trapped inside each cell. Learn more about compression set resistance in foam.
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Are you working on an application requiring a static sealing foam gasket and don't know where to start? Contact us and we'll put you in touch with one of our technical material specialists in your area. We'd love to be the solution to your next problem!