How to choose the right EMI/EMC seal – a guide

Choosing the right EMI gasket is not just about sealing a hatch, door or enclosure. In many designs, the seal also needs to establish electrical contact between two surfaces, attenuate electromagnetic interference and, at the same time, meet requirements relating to, for example, environmental sealing, corrosion protection, compression, service life and installation.

This guide will help you choose the right type of seal based on the application, material, geometry and installation conditions.

When the seal must be both mechanical and electrical

For designers, the choice therefore often comes down to striking a balance between several technical requirements. An EMC seal that works well in an equipment door may not be suitable for a compact electronics enclosure. A solution with high conductivity is not automatically the best choice if the contact pressure is low, tolerances vary or the seal needs to be removed frequently.

What does an EMI/EMC seal do? 

An EMI/EMC seal is used to reduce the risk of electromagnetic interference entering or escaping through openings in a structure. This may include joints in enclosures, doors to electronics cabinets, covers, panels, cable entries or other passages where an electrically conductive barrier needs to remain unbroken. 

In practice, the seal often has to fulfil two purposes at the same time: ensuring electrical continuity between two conductive surfaces, so that the shielding is not interrupted at the joint, and providing a mechanical seal against, for example, dust, moisture, vibrations or other environmental factors. 

That is why the choice of material, profile and installation is so important. A leading seal must be compressed correctly, sit against the right surface and be suited to both the environment and the design. 

Start with the application – not the product type

The most common mistake is to start by asking, “Which gasket is best?” A better starting point is to define what the gasket actually needs to be able to withstand. Ask the following questions:

  • Is the seal to be fitted in an enclosure, hatch, panel, door or cable entry?
  • Are there any requirements regarding environmental sealing, such as protection against dust, moisture or IP rating?
  • How high or low is the contact pressure in the design?
  • Is the seal to be fitted once, or opened and closed repeatedly?
  • Is there a risk of galvanic corrosion between different materials?
  • Is space limited?
  • Should the solution be easy to fit as a retrofit?
  • Do you require customised geometry, length or application?

Once these requirements are clear, it becomes easier to choose between, for example, conductive silicone, knitted gaskets, fabric-over-foam, in-mould assembly or beryllium copper fingers.

Quick guide: which EMC seal is suitable for which application?

Application / requirements Recommended solution Particularly suitable when
Enclosures requiring both EMC and environmental sealing Electrically conductive O-rings and profiles You will need silicone/fluorosilicone, customised profiles and a seal to protect against dust and moisture
Harsh environments and flexible sealing Woven and expanded elastomeric yarns You need high conductivity, an elastomer and a long service life
Seal where conductive wires are to make contact via silicone Directed threads in silicone You need an electrical connector and an environmental seal made from the same material
Low contact pressure and easy installation Conductive fabric over foam gaskets You need flexible EMI gaskets with a foam core and conductive fabric
Doors, hatches and equipment cabinets Knitted gaskets You need robust EMI/RFI shielding, possibly with an elastomeric core or environmental seal
Quick assembly without glue Clip-on knitted RFI/EMI shielding gasket You want a flexible solution for doors, hatches and enclosures
Repeated opening and closing, and high spring-loaded contact pressure Berylliumcopper fingers You need a durable electrical socket in, for example, cupboards, panels or doors
Small details, complex geometries or automated application Electrically conductive elastomer moulded in situ You need the seal to be applied directly to the component or housing

Conductive silicone and fluorosilicone – when environmental sealing is just as important as EMC

An EMC gasket made of silicone or fluorosilicone is often a good choice when the design needs to combine shielding with sealing against, for example, dust, moisture or other environmental factors. The material is flexible, can be moulded into various profiles and is well suited to enclosures, electronics boxes and equipment where space is limited.

Electrically conductive O-rings and profiles are particularly well suited when you need a solution that can be tailored to specific dimensions, profiles and material choices. These may include conductive O-rings, extruded profiles or bespoke silicone EMI gaskets.

Choose this type of solution when:

  • The seal is designed to provide both EMC protection and environmental sealing
  • The design has clear requirements regarding dimensions and compression
  • You’ll need silicone or fluorosilicone
  • there is a risk of corrosion or a harsh environment
  • The gasket is to be integrated into a more advanced housing

Knitted gaskets – a robust solution for doors, hatches and cupboards

Knitted gaskets are often used where the shielding needs to be robust, flexible and able to withstand repeated use. They may be suitable, for example, in electronics cabinets, equipment cabinets, hatches and doors where the seal must establish an electrical connection even when the structure is opened and closed.

Swelex offers several types of knitted gaskets, including combined knitted gaskets with environmental sealing, elastomer-core solutions and solid knitted wire mesh. This makes the product range suitable both when environmental sealing is required and when the focus is on effective shielding and a long service life.

Choose knitted gaskets when:

  • The seal is to be used in doors, hatches or cupboards
  • You need a robust solution for an industrial environment
  • The design requires flexibility and a long service life
  • you want to be able to choose between an environmental seal, an elastomer core or a solid wire mesh
  • Mechanical wear resistance is important

For applications where ease of installation is particularly important, a clip-on knitted RFI/EMI shielding gasket can be a good option. It can be fitted without adhesive and is suitable for doors, hatches and enclosures where quick installation and ease of maintenance are key requirements.

Fabric over foam – for low compression and flexible fitting

Where contact pressure is low or the design involves varying tolerances, a conductive fabric-over-foam gasket may be a good choice. It consists of a foam core covered with a conductive fabric, which provides flexibility and electrical contact even at lower compression levels.

Conductive fabric over foam rubber gaskets is often used in electronics cabinets, equipment cabinets and other industrial environments where the aim is to combine easy installation with effective EMI shielding. The foam core helps the gasket to conform to the surface, whilst the conductive fabric contributes to the shielding.

Choose fabric over foam when:

  • the contact pressure is limited
  • the seal needs to be soft and flexible
  • installation should be straightforward
  • The application requires EMI shielding but not necessarily heavy-duty mechanical sealing
  • You need profiles and dimensions that can be adapted to suit the design

Woven, expanded and targeted wires – when the design requires customisation

In more demanding applications, the seal may need to combine the flexibility of the elastomer with the electrical conductivity of the metal wire. In such cases, woven and expanded wires embedded in elastomers may be a suitable option. They are used when the design requires high electrical conductivity, a flexible seal and adaptation to shape, dimensions and material.

Another solution is targeted silicone wires, in which conductive wires are embedded in silicone or fluorosilicone. This can be a good choice when you need to combine sealing properties with a defined electrical connection between surfaces.

These solutions are particularly suitable when:

  • the seal needs to be customised
  • space is limited
  • There are requirements for both manageability and environmental sealing
  • The choice of material needs to be optimised for the application
  • the design has tight tolerances or specific requirements regarding contact

Form-in-place – when the seal is to be applied directly to the component

In some designs, there is insufficient space, the geometry is unsuitable, or the installation conditions do not allow for a traditional gasket. In such cases, a dispensed, electrically conductive elastomer may be a better alternative.

Electrically conductive elastomer moulded in situ is used when the seal is applied directly to the component or housing. It is particularly suitable for smaller parts, complex geometries or production where repeatable application and precision are essential.

Choose ‘form-in-place’ when:

  • The sealant needs to be applied directly to the part
  • the geometry is complex
  • space is limited
  • you want to reduce the need for separate packaging handling
  • the solution must be adapted to a specific component or enclosure

Beryllium copper contacts – when a spring-loaded electrical connection is essential

Beryllium copper contacts are often used where high electrical contact reliability, spring action and wear resistance are required. They are suitable, for example, for doors, panels, cupboards and other structures where a reliable electrical connection must be maintained over time, even when the structure is in motion or is opened repeatedly.

Unlike softer sealing solutions, beryllium copper contacts rely on spring action. This makes them particularly suitable for applications where contact pressure, service life and mechanical springback are key factors.

Choose beryllium copper fingers when:

  • The connector must be able to withstand repeated opening and closing
  • You need high spring force and electrical continuity
  • The solution is to be fitted to doors, panels or enclosures
  • environmental sealing is not the primary function
  • A long service life and ease of maintenance are important

Bear in mind material combinations and galvanic corrosion

A high-performance seal must not only function electrically; it must also work in conjunction with the other materials in the assembly. If different metals are combined in a damp or exposed environment, galvanic corrosion can become a significant factor.

Therefore, the choice of materials should always be assessed in conjunction with:

  • enclosure material
  • surface treatment
  • environmental exposure
  • service life requirements
  • any moisture, salt, chemicals or temperature fluctuations
  • what type of conductive filler or metal wire is used

This is one of the reasons why it is often worthwhile to discuss the application with a technical specialist before making a final choice of EMC seal.

Don’t forget compression, tolerances and assembly

Even the right material can produce the wrong result if the gasket is not fitted correctly. Insufficient compression can result in a poor electrical connection. Excessive compression can damage the gasket, reduce its service life or make the assembly difficult to fit.

Please note:

  • column width
  • tolerances in the housing and cover
  • recommended compression
  • Surface finish and surface treatment
  • screw spacing or locking mechanism
  • whether the seal is to be fitted using adhesive, tape, clips, grooves or direct application

It is often here that the practical difference between different types of seals becomes apparent. A clip-on solution can simplify installation in a door, whilst an extruded profile may be better suited to a groove. A moulded-in-place seal may be the right choice where the geometry is too complex for a separate seal.

Frequently asked questions about EMI gaskets and EMC seals 

  • What is the difference between an EMI gasket and an EMC seal? 

  • These terms are often used interchangeably. An EMI gasket usually refers to a gasket that attenuates electromagnetic interference. An EMC seal often describes the same type of solution from a systems perspective, where the seal helps the design to achieve electromagnetic compatibility. 

  • Which EMC seal should I choose for an enclosure? 

  • Start by defining the environmental requirements, contact pressure, clearance dimensions, enclosure materials and how often the enclosure is to be opened. For enclosures requiring both shielding and environmental sealing, conductive silicone profiles, O-rings or conductive silicone wires are often suitable options.

  • When is a silicone EMC gasket suitable? 

  • A silicone EMC gasket is ideal when you need to combine electrical conductivity with a flexible seal. It is often used in enclosures, electronics cabinets and other applications where both EMC protection and sealing against dust or moisture are important. 

  • When should I choose knitted gaskets? 

  • Knitted gaskets are a good choice for doors, hatches, equipment cabinets and enclosures where the seal needs to be robust and able to withstand mechanical stress. They are available in versions with an environmental seal, an elastomer core or a solid knitted wire mesh. 

  • When is ‘fabric over foam’ a good choice? 

  • Fabric over foam is suitable when you need a soft, flexible EMI gasket that works at lower contact pressures. It is often easy to fit and works well in electronics cabinets and equipment enclosures.

  • When should I use beryllium copper fingers? 

  • Beryllium copper contacts are ideal when you need a spring-loaded electrical connection, high wear resistance and a long service life. They are often used in doors, panels and enclosures where the connection must be maintained even during repeated opening and closing. 

  • What do you at Swelex need to know in order to recommend the right solution? 

  • It is helpful to be able to describe the application, the materials used in the enclosure, the gap dimensions, the required compression, environmental requirements, shielding requirements, installation requirements and whether the seal will need to be opened frequently. The sooner these requirements are defined, the easier it will be to select the correct EMC seal. 

     

     

     

When should you seek help with your choice?

You should seek technical assistance at an early stage if the design has several concurrent requirements, such as EMC shielding, IP rating, low compression, risk of corrosion and limited space. The same applies if the solution is to form part of a larger product platform or if the seal needs to be adapted to specific dimensions.

Swelex specialises in premium products and bespoke solutions for the electronics, industrial and technical sectors, where the right choice of materials is crucial. This means you can receive support in selecting the right product range, the right material and the right design before the final design is confirmed.

Do you need help choosing the right EMI gasket or EMC seal? Contact Swelex for technical advice, help with material selection and to request a quote.

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