Silicone sponge is one of Jehbco’s most unique materials, finding applications in a variety of industrial applications from lighting gaskets to dry seals and oven manufacturing. The most important feature of a closed-cell silicone sponge is its extreme compressibility, which allows it to form airtight seals with very low sealing loads. This feature combined with silicone’s naturally ability to withstand high and low temperatures (-60°C to 200°C) and the increased insulating properties of sponge rubber makes silicone sponge an exceptionally versatile elastomer suitable for many different applications.
Silicone sponge is what is known as an expanded elastomer. Many elastomers can be formulated into a kind of sponge by incorporating air into the bulk of the elastomer during the manufacturing process. Typically, this air is visible on the final product as well-dispersed bubbles, which can vary in size depending on the cell structure. This incorporation of air increases the softness and compressibility of the elastomer while simultaneously lowering its density. The amount of air and overall consistency of the air inclusions determines the cell structure of the sponge, which has significant impact on the mechanical properties of the final sponge.
Two different kinds of sponge rubber can be made depending on the cell structure of the sponge itself. The first is called an open-cell sponge, which is the same kind of cell structure as the sponges used for dishwashing. In an open-cell sponge, all the inclusions of air are connected by channels, which allows fluids to flow through the sponge. This is crucial when the absorption or passage of fluids through the sponge is required for the desired application. Open-cell sponges can be very heavily compressed upon the application of pressure and will expand back readily as air can easily flow back into the air pockets of the material. However, open-cell sponge is not suitable for the formation of air-tight seals.
In a closed-cell silicone sponge, all the inclusions of air are completely enclosed by rubber. This means that the air inclusions are completely inaccessible to any fluids or microorganisms. These air pockets can still be deformed by the application of pressure, in the same fashion as a rubber ball can be compressed, providing significantly improved compressibility over solid silicone. This allows air-tight seals to be easily formed. To maximise compressibility and also improve the appearance of the sponge, smaller, more consistently shaped and dispersed air inclusions will form a higher quality sponge rubber. In accordance with ASTM D1056, a closed cell sponge must not absorb more than 5% of its weight in water, while a sponge that absorbs more than this value is classified as open-cell.
Typically, closed-cell sponge rubber is made using a chemical blowing agent, which decomposes during the curing process to produce gas, which mechanically expands to form small inclusions in the bulk rubber. Over time, air slowly through the bulk of the silicone, replacing these gasses with air. However, due to the unique chemistry and processing temperatures of silicone rubber, many traditional blowing agents are chemically incompatible with silicones. Typically, silicone sponge employs a peroxide curing system together with a carefully formulated mix of additives and blowing agents to produce a high quality closed-cell silicone sponge with a low density and a consistent cell structure. As can be expected, the blowing process causes severe expansion of the silicone profile, so it is extremely difficult to manufacture specific profiles. Jehbco is one of few silicone manufacturers that have dedicated extensive amounts of research and resources to perfecting the sponge making process so that even the most intricate custom profiles can be made. Jehbco’s sponge can be made into a wide range of profiles, or custom-made to suit your requirements, and is available in three softness grades (soft, medium and firm) depending on your preferences.
Ultimately, if you are looking for a soft, low-density material with excellent compressibility and extreme chemical and heat stability, enquire about our closed-cell silicone sponge. Jehbco has spent many years formulating and developing closed-cell silicone sponge and have consistently impressed our customers with our high-quality sponge rubber. For help selecting a material for your application, consult our applications page and contact us with any questions.