A Complete Guide to Sponge Rubber

Sponge rubber, also known as expanded foam rubber, is a versatile and resilient material that finds widespread use across various industries. Made from synthetic rubber and silicone compounds, sponge rubber has an expanded cellular construction that is flexible and compressible. It is commonly manufactured with a closed-cell structure so does not absorb water and can be used to stop water ingress. Sponge seals manufactured from these materials demonstrate a level of durability that meets the demanding requirements of a diverse range of sealing applications. As well as being suitable for creating watertight seals, it can also be used for shock-absorbing and cushioning.

Due to its unique set of characteristics, sponge rubber can be extruded to create bespoke sealing solutions, cut into strips or manufactured into complex gaskets. These can be supplied with and without adhesive backing.

This guide explains the process for manufacturing sponge rubber seals, and discusses the advantages and disadvantages of using this material in sealing applications.

Sponge seals can be manufactured from a large range of materials and offer a reliable general purpose solution for most sealing applications. Allowing for the creation of seals that aim to stop water ingress, sponge rubber offers a unique set of properties that cannot be found in solid rubber. Some of the advantages that make sponge rubber a dependable material include;

One of the key benefits of sponge rubber is its ability to compress and fill irregular gaps. When positioned between two surfaces, sponge sections are fairly soft so easily squash to create seals that stop the ingress of water, dirt and air. A sponge seal should return to its original shape and dimensions once the compression has been removed. However, excessive compression may cause permanent deformation of the seal. This is known as compression set which refers to the deformation or loss of thickness experienced by a material that has been subjected to excess force over an extended period of time. Compression set can be avoided by adjusting the compression force so that the sponge section is compressed by approximately a third.

The force required to compress seals manufactured from sponge rubber is determined by the construction of the section and type of material used. With low closing forces, it is often necessary to use a profile that has a hollow centre. This aids compression and makes the seal significantly easier to compress. Sponge rubber can also be manufactured in a selection of densities which influences its hardness.

Sponge rubber can be manufactured with either an open or closed-cell structure. Whilst both materials present a similar appearance, they have very different properties that make them suitable for different applications. Open-cell sponge is softer, permeable to water and has less resistance to compression. This is useful for applications such as absorbing and reducing sound, but has obvious limitations for creating reliable watertight seals.

Closed-cell sponge has a structure that prevents the passage of air, water and other fluids which makes it resistant to the absorption of liquids and gasses. This is ideal for sealing solutions in both exterior and interior applications that are installed to act as a barrier to moisture, heat and sound. Closed-cell sponge rubber also has a tendency to recover to its original shape and size more effectively after compression.

The majority of products manufactured from closed-cell sponge rubber materials are used as sealing solutions that aim to prevent water ingress. As closed-cell sponge is inherently resistant to the absorption of water and other fluids, it is suitable for outdoor sealing applications, as well as in environments where exposure to moisture is a concern.

The weather resistance properties of a particular sponge rubber section will be dependent on the material that it has been manufactured from. However, due to its relatively low price and desirable characteristics, most sponge seals are made from EPDM which is able to withstand exposure to weathering, ozone and UV.

The density and weight of sponge rubber, whether in open-cell or closed-cell form, is lower than comparable materials, such as solid rubber, plastic and metal. The lightweight nature of sponge is advantageous in industries where weight is a critical factor. As most sponge seals are made from closed-cell materials, they are also buoyant and suitable for flotation devices or marine applications.

The flexibility of sponge rubber is a result of its cellular structure. Closed-cell sponge has a resilient feel that provides a degree of stiffness while retaining flexibility. This allows the material to conform to irregular surfaces.

The type and formulation of sponge rubber can be tailored to meet specific requirements, allowing for a wide range of hardness, flexibility and other properties. As each type of rubber has a unique set of characteristics, it is possible to select a material that is suitable for the environment that it will be used in, as well as any substances that it may come into contact with. This includes applications requiring a sealing product that is resistant to heat, chemicals or weathering. 

It is also possible to add pigments to some silicone and rubber compounds to create sponge seals in various colours. This is desirable for applications that need to match company branding or provide an aesthetic appearance.

Sponge rubber is a type of product that can be manufactured from various rubber and silicone compounds. The choice of sponge rubber depends on factors such as the intended use, environmental conditions and required performance. These materials have different characteristics and choosing the correct compound is essential for providing a long-lasting sealing solution that does not degrade or deteriorate. It is possible for these compounds to be blended to create hybrid rubber materials with enhanced properties or lower production costs. Some common types of sponge rubber include;