The terms sponge and foam are used interchangeably but they’re not the same. Buy foam for a gasket application and you may find the joint leaks. Use sponge material for cushioning and you may not get the protection you expected. Sponge and foam both have cellular structures, but there are important differences between the two.
Different Processes
Producing foam material is similar to baking bread. A chemical reaction in the liquid mixture creates carbon dioxide gas that leaves a very open structure.
Sponge materials also use a chemical reaction to create gas bubbles, but these remain self-contained cells, each one isolated from its neighbors. Some manufacturers can control the size and distribution of these pores to produce very consistent material with highly predictable behavior.
Open and Closed
The foam production process leaves an open structure more like a mesh than a solid. The stiffness or rigidity of this structure depends on the polymer used – typically that’s PVC, polyethylene or polyurethane.
In contrast, in a sponge the pores influence material behavior. Unlike a foam material, when sponge is compressed the gas in each pore has nowhere to go. That results in strong compression set resistance and good compression recovery.
Sealing Properties
Foam and sponge materials both have the advantage of low density but behave very differently when asked to act as a barrier. The open cellular structure of foam material lets fluid pass through readily, even when compressed. Sponge however blocks the movement of gases and liquids. That makes sponge material a good choice in HVAC sealing applications.
Cutting sponge will open up the edge pores. This allows a limited amount of liquid retention but the body of the material still acts as a barrier.
Materials for Sponge Gaskets
Practically all elastomers can be manufactured with a closed cellular structure. Consequently, neoprene, EPDM, nitrile and silicone gasket material are all available as sponges. As with their solid variants, these can be purchased with varying levels of temperature resistance and strength. Talk to a material specialist at Hennig Gasket if you need more advice.
