Sponge rubber and cellular rubber are rubber-based materials used mainly for insulation and sealing.
Sponge rubber and cellular rubber are made from the same raw materials, namely natural and/or synthetic rubbers, producing different material properties depending on their mixture. The material structures of sponge rubber and cellular rubber are fundamentally different, however, due to the different production processes.
Sponge rubber has a mixed cellular structure with mostly open cells and a dense outer skin. Cellular rubber, on the other hand, has a closed cellular structure with no outer skin. Both materials are primarily used for sealing and insulating, as well as eliminating rattle and buzz.
Sponge rubber is made of foamed rubber and has a mixed cellular structure with mostly open cells and a closed outer skin. The dense, robust, and elastic outer skin lends the surface of sponge rubber a generally better protection compared with cellular rubber. The outer skin also provides excellent sealing properties. If the surface is damaged, however, the material can become saturated with liquid due to its open cells. The mixed cellular structure of sponge rubber ensures high compression elasticity and good recovery. The material firmly adapts to all surrounding surfaces under slight pressure, thus creating a seal.
Cellular rubber is a closed-cell type of rubber that is produced in an expansion process. The cells in the material interior are therefore not connected to each other. In contrast to sponge rubber, cellular rubber consequently does not need an outer skin in order to be used as a seal. The cellular rubber block does have a fabrication skin, which is essentially non-functional however and is removed as a waste product during subsequent processing. Due to the lack of an outer skin, the surface of cellular rubber is more sensitive and easier to damage than that of sponge rubber. Nevertheless, neither gases nor liquids can penetrate the closed cells. Cellular rubber is therefore practically air- and water-tight.
Different mixtures can have an influence on the strength and other properties of the materials. The various natural and/or synthetic rubbers provide the base structure for rubber mixtures. The final properties are determined by further additives such as fillers, softeners, ageing inhibitors, and cross-linking chemicals. Rubber mixtures are differentiated into four main groups:
Natural rubber (NR) is suitable for normal technical applications without particularly strict requirements. It is characterised by high elasticity and good cold behaviour. Ethylene-propylene-diene rubber (EPDM) is suitable for outdoor use and is highly resistant to ageing, ozone, light, weathering, and temperature. Chloroprene rubber (CR) is suitable for strict requirements with respect to temperature, flammability, and resistance to oils, greases, acids, and bases. It is also highly resistant to ageing, ozone, and weathering. Nitrile rubber (NBR) is resistant to oils, greases, and to gasoline to some extent, but is flammable. In addition, it is characterised by very good resistance to ozone and weathering.
The macro images on this page are intended to provide an overview of the special features of different foam materials. For the sake of clarifying the differences in cell size and structure, the same image excerpt is used throughout. Of course, many other types are available than those highlighted.