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Colored Sponge Compounds

Some applications require a non-black or even a color-specific sponge solution, with the same technical benefits and physical properties normally achieved with traditional black sponge compounds.

Quanex Custom Mixing (QCM) has the capability to color match a sponge system to nearly any color standard, and we can provide consultation on how best to ensure a high quality, and consistent final product.

We know product engineers rely on material science to help them drive innovation in design, quality, construction, and performance of products across every industry on a worldwide scale. QCM develops compounds designed to meet the needs of stringent quality assurance programs to support leaders in a variety of markets including automotive, building and construction, belting and hose, agriculture, medical, and energy. We combine best-in-class service with industry-leading manufacturing technology.

QCM has a deep-rooted history and experience in the design and manufacturing of sponge compounds, which has made sponge one of our core product lines. Success in sponge requires excellent control over incoming raw materials, precise weighment of formulation additives and incredible control throughout the entire mixing process. QCM offers a wide array of sponge compound solutions for both continuous extrusion and molding processes.

What is sponge compound?

Sponge rubber compounds use a blowing agent to create a cellular structure within the rubber matrix during the curing process. The blowing agent transforms into a gas, generating bubbles that expand the rubber material into a cellular sponge. The cell structure created by the blowing agent reduces the overall hardness and density of the compound, making it lighter and more flexible.


Sponge rubber compounds can be used for a variety of applications and are best suited for applications that require compression and flexibility in creating a seal, which often cannot be achieved with solid (dense) rubber or other rigid material. Some specific applications include outdoor weather seals for recreational vehicles and equipment, foam grips, good container seals, appliance seals, drum gaskets, residential and commercial weather-stripping, window spacers, and insulation.

Product Design Considerations

Components crafted from sponge rubber compounds can take advantage of the specific attributes native to sponge to meet desired product specifications. Open versus closed cell sponge can have very different compression rates and will function quite differently in the final product.

Material design is key in achieving the desired open-cell or closed-cell properties, which are largely controlled by the compound’s cure rate and selection of blowing agents used in the formulation.

Open-cell sponge rubber has distinct cells that are interconnected to neighboring cells. There are no discreet and separated individual cell walls. This network of elastic rubber tunnels allows air to easily re-inflate the sponge article once a deforming force is removed, enabling the article to rapidly regain its original physical form and dimension. Open-cell rubber is often an ideal choice for sound damping and cushioning applications.

Closed-cell sponge rubber consists of individual cells, each with its own elastomeric wall that separates it from the other. Closed-cell sponge often exhibits slower recovery when compressed compared to open cell sponge. This is because when compressed, gases must slowly re-permeate the individual cell walls to re-inflate the individual cell.

Manufacturing Considerations

Open-cell and closed-cell sponge are typically produced by very different processes, which can be an important consideration when determining which type of sponge rubber to use for your product.

Open-cell sponge rubber is usually manufactured in sheets or press-molded articles.

Closed-cell sponge can also be molded, but is most commonly produced into profiles via continuous extrusion processes. In special cases, it can be press molded and oven-expanded into large rubber “bunstock” and then later scythed into uniform sheets for die cutting.

Color Considerations

Color matching is achieved by adding organic and inorganic pigments to a non-black sponge rubber base. Color control can be enhanced by utilizing pre-dispersed and polymer-bound pigment color concentrates. These tend to be cleaner and more efficient to weigh up, and minimize the risk of fly loss during mixing which provides excellent color control and consistency batch to batch. Color stability can be affected by the quality and consistency of raw materials. Light colors and color-critical applications often require the use of a light colored UV and heat stable plasticizers as well as a small amount of TiO2 to keep the base color of the compound uniform.

Yellowing can be a common challenge, particularly when dealing with very lighter colored sponge. Care must be taken when selecting the type and amount of curatives and blowing agents used in the formulation. Choosing a peroxide cure system in lieu of a sulfur cure system can prevent the risk of yellowing altogether. Using clean, bright mineral fillers can also help mitigate yellowing, and preserve the exact color match required.

Why choose QCM?

Quanex Custom Mixing has over 20 years of experience in designing and mixing sponge rubber formulations. We leverage that experience in being able to provide superior color consistency with non-black colored sponge compounds. Customers choose QCM because of the high quality of the final product, allowing an exact match of the provided color sample coupled with exceptionally uniform cell structure, and smooth surface quality.

QCM continues to build on its reputation in the market for providing consistent products. When it comes to colored sponge, our design team has the capability to create a custom color solution, our control systems ensure that our colored compounds are the same every time, and our technical experience allows us to reduce variables that can alter color stability over time. All of these are paramount to our success and the success of our clients.

For information on Quanex Custom Mixing non-black colored sponge, contact us.

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