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24 Jul 2024

Exploring the Benefits of Sponge Rubber Extrusions

Sponge rubber, also known as expanded foam rubber, is a specific rubber structure containing tiny pockets of air. Sponge rubber can be made from many of the same compounds as solid rubber. But thanks to its unique structure, sponge rubber can be used where solid rubber is too heavy and dense or where applications need special insulation, shock absorption, or even water-filtering capabilities. In this guide, we cover everything about sponge rubber extrusions.

What Are Sponge Rubber Extrusions?

Like other rubber extrusions, sponge extrusions are created by forcing material through a die that determines a specific profile shape. However, sponge rubber undergoes an additional curing step, which causes the rubber to expand and creates its characteristic sponge-like texture.

Sponge rubber has distinct characteristics that make it suited to specific applications. It’s more porous, flexible, and lightweight than solid rubber alternatives.

Sponge rubber comes in open-cell or closed-cell structures:

The open-cell structure features interconnected cells which allow air, water, and other fluids to pass through, making it good for breathability.
The closed-cell structure features sealed cells that prevent fluid passage to offer better insulation and water resistance.

The sponge-like structure of this type of rubber allows it to be compressed significantly, making it ideal for use in cushioning, shock absorption, and insulating applications. Due to its cellular structure, sponge rubber extrusions are much lighter than solid rubber alternatives and provide excellent thermal and acoustic insulation properties. Because of this, sponge rubber is used in HVAC systems, construction, and automotive applications often.

Thanks to rubber extrusion's versatility, sponge rubber can be extruded into a wide range of shapes and sizes, including complex profiles.

Key Applications in Modern Engineering

Sealing and Gasketing

Sponge rubber is used in door and window seals, as well as gaskets for automotive and marine applications.

Why sponge rubber?

Compressibility allows the rubber to fill gaps and conform to irregular surfaces, providing a better seal against water and air.
Sponge rubber can return to its original shape easily, maintaining integrity through repeated uses.
Some sponge rubber, like nitrile rubber, is composed of a compound that resists oils, chemicals, and solvents, making it reliable in harsh conditions.

Cushioning and Padding

Sponge rubber is used in packaging materials, other protective padding, and products like anti-fatigue mats.

Why sponge rubber?

Sponge rubber absorbs and dissipates energy, creating a barrier that protects other items from impacts and reduces strain on their surfaces.
Sponge rubber is available in various densities, which means the appropriate level of cushioning can be tailored to the application without excessive bulk.

Filtering

Sponge rubber can be bespoke-made to either facilitate or block air and water passage in applications.

The porous structure of sponge rubber either effectively filters water and air (open cell) or prevents it (closed cell) while filtering out larger particles.
Sponge rubber's resistance to chemical and physical wear and pliable, shapeable nature make it highly reliable in filtration.

Other applications which use sponge rubber include:

Vibration dampening in machinery mounts, eclectic equipment, and automotive components.
Weatherstripping for commercial doors and window seals.
Soundproofing in building construction, appliances, and automotive applications.
Thermal insulation in HVAC systems, thermal barriers, and refrigeration units.

Advantages Over Solid Rubber Extrusions

Solid and sponge rubber are both elastomers—natural or synthetic polymers with elastic properties. They are available in many of the same compounds, including EPDM, silicone, and neoprene, and they can be extruded into various shapes. The key difference between solid and sponge rubber is air.

The structure of sponge rubber consists of cells that act like little balloons. These cells either hold air or permit its passage. While both solid rubber and sponge rubber provide sealing and insulation, only sponge rubber provides better cushioning, while solid rubber provides better impact resistance.

Let’s review the other differences between sponge rubber and solid rubber.

Feature	Solid Rubber	Sponge Rubber
Air Content	No cellular structures	Balloon-like cellular structures/interconnected air pockets
Durometer (Hardness)	Ranges from soft to hard.	Available in various durometers; usually softer, but not always.
Density	High density: good for resistance to wear and tear.	Low density: good for lightweight cushioning and insulation.
Applications	Used in vehicles, machinery, and equipment. Absorbs impacts at loading docks and other areas. Protects mechanical parts and reduces downtime. Provides surface protection and fluid containment. Redirects sound waves in various industrial applications.	Used in a variety of cushioning applications. Reduces vibrations in machinery and equipment. Seals against environmental elements. Absorbs sound for noise reduction. Used in insulating applications to retain or block heat. Employed in filtering air, water, and other substances.

Customisation and Manufacturing Processes

You can find out about the process of creating solid rubber extrusions in our article Understanding Rubber Extrusions: A Comprehensive Guide. Here, we detail what happens in the manufacturing process of sponge rubber extrusions. Although the general process is much the same, some key differences give the end product its distinct spongey quality. See below.

Stage	Solid Rubber Extrusion	Sponge Rubber Extrusion
Preparing the material	The base rubber compound is mixed with required additives, curing agents, stabilisers, or fillers.	A blowing agent, a foaming agent responsible for creating the distinct cellular structure of sponge rubber, is added to the base rubber compound along with other typical additives.
The physical extrusion process	The material is fed into the extruder and forced through a die to create a specific extruded shape.	This process is the same as that of solid rubber. However, the presence of the blowing agent requires precise temperature control to activate it properly.
Activating the blowing agent	No need for a blowing agent.	During the extrusion process, the blowing agent is activated by temperature. This causes it to decompose, releasing gases (usually nitrogen or carbon dioxide) that create bubbles in the rubber matrix, resulting in its characteristic spongey structure.
The curing process	Curing occurs in a continuous vulcanisation process using a salt bath, steam, or hot air.	The curing stage is often two-fold to accommodate the expansion and stabilisation of the sponge rubber. Pre-gel stage: partial curing at low temperature to allow the cellular structure to be created. Final cure: curing at high temperature to stabilise the structure and ensure complete vulcanisation.

Summary of Differences in the Sponge Rubber Extrusion Process

Difference	Details
Addition of blowing agent	The critical difference that sponge rubber includes a blowing agent to create the cellular structure.
Temperature control	More precise temperature management to activate the blowing agent and ensure proper cell formation.
Two-stage curing	Often involves a pre-gel stage to allow cell formation, followed by a final curing stage.

Trends in Sponge Rubber Extrusions

Sustainable and Eco-Friendly Materials

Using sustainable materials in sponge rubber extrusion is a growing trend. These materials are being used in sponge rubber compounds to improve biodegradability. For example, a study on creating a green composite sponge of natural rubber reinforced with cellulose filler using alginate as a dispersing agent showed improved mechanical properties, higher water absorption, and better biodegradability: “sufficiently biodegraded in soil for about 21–27 % in120 days.”

Manufacturers are increasingly adopting biodegradable and recyclable rubber compounds in response to the rising consumer demand for environmentally friendly products. This shift reflects sustainability demands and adherence to global regulations.

The Demand for Customisation

With advancements in digital technologies and e-commerce, there is an increasing demand for customised and personalised sponge rubber products. Consumers and industries alike seek specific characteristics such as unique shapes, sizes, and performance attributes tailored to their precise needs.

The extrusion process is ideal for supporting this. The rubber extrusion profile is determined by a die, a disk with a recess in the shape of the rubber profile through which the rubber is forced. Dies can be cut to any shape, no matter how specific or complex (to an extent), meaning the demand for highly customised shapes can be met with extrusion.

Increased Demand in The Automotive Industry

The automotive industry's push for lightweight and fuel-efficient vehicles drives increased demand for sponge rubber extrusions. Due to their lightweight nature and excellent performance characteristics, sponge rubber components are used extensively for seals, gaskets, and vibration dampening. This trend is leading to continuous improvements in extrusion processes and material quality to meet the stringent requirements of the automotive sector.

A report from Market Research Future indicated that the automotive sponge rubber market is projected to grow from USD 46.77 billion in 2024 to USD 92.50 billion by 2032, exhibiting a compound annual growth rate (CAGR) of 8.90% during the forecast period (2024 - 2032). This growth is driven by the need for lightweight and fuel-efficient vehicle components.

Browse our rubber products, which include extrusions, profiles, fabrications, and mouldings. Or take a look at other guides in our blog about different types of rubber extrusions and their uses.