When to Use a Fabric-Over-Foam Gasket, or Conductive Fabric Gasket

Key Points

• Understanding Conductive Fabric Gaskets: Conductive fabric gaskets, also known as fabric-over-foam gaskets, are designed to provide electrical conductivity and reduce electromagnetic interference (EMI) between surfaces. They are essential in various applications, including aerospace, defense, and medical devices.
• Key Considerations for Selection: When choosing between conductive fabric gaskets and conductive elastomers, factors such as compression requirements, space and weight constraints, environmental conditions, and shielding performance are crucial in determining the best fit for your specific application.
• Advantages and Limitations: Conductive fabric gaskets offer flexibility and effective EMI shielding but may have limitations in terms of chemical resistance and long-term compression set. Understanding these factors can help you make informed decisions for your project.

Here at Modus Advanced, we truly enjoy getting involved with our customers early in the design phase for their projects. It gives us the opportunity to build trust and to iterate on design with our customers to ensure their part is crafted with speed and precision – the Modus way.

This article will provide insight into the world of conductive fabric gaskets, which are referred to in the industry as fabric-over-foam gaskets. We'll cover when and where to use them, and a few critical considerations in selecting them as your gasket of choice.

Let’s get to it.

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Everything you've ever wanted to know about EMI gasket design

What is a Conductive Fabric Gasket?

A conductive fabric gasket, more commonly referred to as a fabric-over-foam gasket, is almost as straightforward as it sounds: it's a type of EMI gasket that is made of conductive material, either a fabric or a foam, that has been coated or infused with conductive materials such as metal particles or carbon.

This type of gasket is designed to provide electrical conductivity between two surfaces, typically in electronic devices or equipment where electromagnetic interference (EMI) needs to be minimized. The need for this type of gasket extends across many different applications – everything from aerospace and defense to medical devices and space exploration.

An effective conductive fabric gasket works by creating a conductive path between two mating surfaces. This seal reduces the EMI that can occur between the two surfaces, and restricts ingress and egress of EMI. The gasket is used to provide a seal that is both conductive and flexible.

These types of gaskets are most commonly used in applications that require shielding against  radio frequency interference (RFI) and electromagnetic interference (EMI) and are ubiquitous in industries such as the aerospace and defense, medical device, and emerging technology categories where electromagnetic shielding is critical.

Conductive Fabric Gaskets vs. Fabric-Over-Foam Gaskets

Chances are that you landed here via a search using the terms "conductive fabric gasket". We're certain you've found what you're looking for, but it's worth noting that while search engines brought you here, there is a different term used within the industry for these types of gaskets – fabric-over-foam gaskets.

They are indeed the same thing, but the technical term provides a better understanding of the outward physical properties of the gasket. The fabric-over-foam construction is what gives these gaskets their unique properties and makes them suitable for various EMI shielding applications.

Conductive Elastomers vs. Conductive Fabric Gaskets

Conductive elastomers and conductive fabric gaskets (fabric-over-foam gaskets) are two types of custom gaskets used to provide EMI/RFI shielding between mating surfaces in electronic devices. While they're both intended to do similar things, there are a few key differences between them that can impact your decision-making.

Conductive elastomers are made from silicone rubber or other elastomeric materials that have conductive particles distributed throughout the material. Silver or nickel are among the most commonly used conductive materials.

These elastomers are effectively flexible and can be molded into many different shapes and sizes to fit the needs of your particular device. They're ideal for applications where a custom fit is needed. Conductive elastomers are also highly effective at providing EMI/RFI shielding and can withstand a wide range of temperatures and environmental conditions that are present in many industries such as defense and aerospace.

Alternatively, conductive fabric gaskets are made from fabric that has been coated with or had conductive particles distributed throughout it which is placed over a conductive foam core. These gaskets are typically more compressible than their conductive elastomer counterpart, which makes them ideal for applications that require a high degree of flexibility.

Conductive fabric gaskets are also effective at providing EMI/RFI shielding and are often used in applications where weight and space constraints are critical (perhaps in… space applications).

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EMI Shielding Resource Center

Making the Choice

Your specific application will dictate the requirements needed for your conductive gasket, but that doesn't mean it will always be an obvious choice. Here are some factors to consider when deciding between the two:

1. Compression Requirements: Conductive elastomer gaskets are better suited for environments that require a higher degree of compression for longer periods of time. They're also a better choice for sealing surfaces that are uneven or rough. Conductive fabric gaskets, on the other hand, are more compressible and can conform better to surfaces with less compression force. This low compression characteristic makes fabric-over-foam gaskets ideal for applications where minimal closure force is available.
2. Space and Weight Constraints: If space and weight are a concern, when you're heading to space for example, the conductive fabric gaskets are thinner and lighter making them a better choice. The foam core in fabric-over-foam gaskets contributes to their lightweight nature while still providing excellent EMI shielding properties.
3. Environmental Factors: Conductive elastomer gaskets are typically more forgiving (and effective) when it comes to extreme temperatures, moisture, and other environmental factors. However, some fabric-over-foam gaskets can be treated with special coatings to enhance their environmental resistance.
4. Shielding Performance: While both types of gaskets offer EMI/RFI shielding, the shielding performance can be affected by the composition of the conductive materials used in the gasket. In general, conductive elastomer gaskets offer better shielding effectiveness in lower frequency ranges, while conductive fabric gaskets are more effective in higher frequency ranges.
5. Customization: Conductive elastomer gaskets are easily customizable, while fabric-over-foam gaskets are typically available in standard sizes and shapes (which is great for rapid production). However, custom gaskets can be manufactured to meet specific requirements when needed.

The choice between the two really comes down to the specific requirements of the application. Working with a trusted manufacturing partner such as Modus can significantly alleviate any headaches associated with analysis paralysis in the design phase.

Advantages and Limitations of Conductive Fabric Gaskets

Conductive fabric gaskets may not be the right choice for every application, but there are several reasons to consider them when you are iterating through the decision-making process:

1. Flexibility: Conductive fabric gaskets are incredibly flexible, allowing them to conform to irregular surfaces, absorb vibrations, and provide a tight seal even under compression. They may be a good fit for complex geometries as well.
2. EMI shielding performance: The flexibility offered by conductive fabric gaskets allows it to provide a better seal against EMI/RFI in certain applications compared to other gasket materials. The conductive fabric layer ensures consistent electrical contact across the entire surface.
3. Better thermal management properties in high-temperature environments: Conductive fabric gaskets can dissipate heat more efficiently, providing better thermal management in high-temperature environments.
4. Low compression force: Fabric-over-foam gaskets typically require less compression force to achieve an effective seal, making them suitable for applications where minimal closure force is available.
5. Lightweight: The foam core in fabric-over-foam gaskets contributes to their lightweight nature, making them ideal for aerospace and portable electronic applications.

This all sounds promising; however, there are some limitations of conductive fabric gaskets which may render them inappropriate for your project:

1. Lower compression set and resilience compared to conductive elastomers: This means that over time, the gasket may lose its ability to compress and seal properly, leading to leaks and reduced performance.
2. Limited chemical resistance: They may degrade or break down when exposed to certain chemicals, leading to reduced performance and shorter lifespan. However, some manufacturers offer special coatings to improve chemical resistance.
3. Less suitable for applications that require high-force compression or high-frequency EMI shielding: While they are highly flexible and can conform to irregular surfaces, they may not provide sufficient compression force for applications that require a tight seal or high-frequency EMI/RFI shielding.

Additional Considerations for EMI Shielding Gaskets

When selecting an EMI shielding gasket, whether it's a fabric-over-foam gasket or a conductive elastomer, there are several additional factors to consider:

1. Frequency Range: Different materials and designs perform better at specific frequency ranges. Ensure that the gasket you choose is effective for the frequencies you need to shield against.
2. Shielding Effectiveness: This is typically measured in decibels (dB) and indicates how well the gasket attenuates electromagnetic radiation. Higher dB values indicate better shielding performance.
3. Galvanic Corrosion: When two dissimilar metals come into contact in the presence of an electrolyte (like moisture), galvanic corrosion can occur. Consider the materials of your enclosure and the gasket to avoid this issue.
4. Compression Set: This refers to the gasket's ability to return to its original thickness after compression. A lower compression set is generally desirable for long-term performance.
5. Operating Temperature Range: Ensure the gasket can withstand the temperature extremes of your application without degrading or losing its shielding effectiveness.
6. Flame Resistance: In some applications, particularly in aerospace and defense, flame resistance may be a crucial factor.
7. Outgassing: For space applications or sensitive electronic equipment, low outgassing materials may be necessary to prevent contamination.

Alternative EMI Shielding Solutions

While fabric-over-foam gaskets and conductive elastomers are popular choices for EMI shielding, there are other options available depending on your specific needs:

1. EMI Shielding Tape: This adhesive-backed tape is useful for quick fixes or prototyping. It's easy to apply and can be an effective solution for covering small gaps or seams in enclosures.
2. Conductive Foam Gaskets: These gaskets are made entirely of conductive foam and can be a good choice when a softer, more compressible option is needed.
3. Mesh Gaskets: Made from knitted wire mesh, these gaskets offer excellent shielding effectiveness and are particularly useful in high-temperature applications.
4. Form-In-Place (FIP) Gaskets: These gaskets are dispensed as a liquid and cure in place, allowing for precise application in complex geometries.
5. Metallic Gaskets: For extreme environments or very high shielding requirements, solid metal gaskets may be necessary.

Choosing the Right Conductive Fabric Gasket for Your Application

We've covered what conductive fabric gaskets/fabric-over-foam gaskets are, how they work, and their applications. Depending on your application and requirements, this type of gasket may be the answer to your EMI shielding needs.

When selecting a fabric-over-foam gasket, consider the following:

1. Conductive Fabric Material: Common options include nickel-copper, silver-copper, and aluminum-copper fabrics. Each has different conductivity and corrosion resistance properties.
2. Foam Core: The type of foam used (e.g., polyurethane, silicone) affects the gasket's compression characteristics and environmental resistance.
3. Thickness: The overall thickness of the gasket impacts its compressibility and ability to fill gaps.
4. Adhesive Backing: Some fabric-over-foam gaskets come with an adhesive backing for easy installation.
5. Protective Coatings: Certain manufacturers offer protective top coatings to enhance durability and environmental resistance.

If you're still unsure of where to go next, reach out to the expert engineering team at Modus Advanced. We're ready to partner with you in bringing your life-changing and life-saving projects to life. Our experience with EMI shielding solutions, including fabric-over-foam gaskets, conductive elastomers, and other shielding products, allows us to guide you towards the best solution for your specific application.

Remember, the right EMI shielding gasket can make all the difference in your product's performance and reliability. Don't hesitate to seek expert advice to ensure you're making the best choice for your unique requirements.