There are two major classifications of all types of foams – open cell foams and closed cell foams. The distinction between the two is a very important design consideration. The wrong type can and will cause a failure in the performance of the part.
Open cell foams are foams that simply allow the passage of water and air through the cells. An example of an open cell foam application is an air filter, or a dust seal. Open cell foams do not provide a water seal.
Closed cell foams are foams that provide a seal against the flow of water. An example of a closed seal would be a gasket on a car taillight, or a water seal on a house window frame. Closed cell foams will provide a water seal when compressed, typically a minimum of 30%. One water seal test method is a U channel test where 1 strip of closed cell foam is sandwiched between 2 pieces of glass in a “U” configuration and the channel is filled with water. Performance is measured based upon any migration of water past the “U” channel over time. It is important to note that in any closed cell foam sealing application that the water seal is dependent upon the compression of the foam, not on any adhesive that may be applied to the foam.
Closed cell foams and open cell foams are also used for other applications other than sealing, including for insulation, and for composite cores. There are merits for both types of these types of foams depending upon the cost performance requirements of the application. Some of these merits are discussed elsewhere in this website.
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