Solid and foam materials can be made from several of the same polymer families, but their structures behave differently. The choice depends on compression, gap variation, strength and the intended sealing or cushioning function.
Solid rubber
Solid rubber is used where strength, dimensional stability and compression resistance are required. Molding or sheet conversion can produce shaped seals, gaskets and non-standard components.
Foam structure
Foam offers a lighter, softer structure and can conform to gaps while providing cushioning. Closed-cell materials are often considered for sealing against water and dust. Open-cell grades are considered for functions such as sound absorption and filtering, depending on the particular material.
Design for the working gap
The installed compression, thickness, density, adhesive and support layers should be considered together. A soft foam and a solid layer can also be laminated where the application needs both conformability and support. Select and test the specific grade instead of assuming that all foam behaves alike.