Signal interference is a silent troublemaker in modern electronics. From high-speed data lines to medical and audio-visual systems, even a small burst of electromagnetic noise can distort performance.
Cable shielding – also called screened cable in the UK – solves this by wrapping conductors in a conductive barrier that keeps signals clean and stable.
Below, we look at the main types of cable shielding, how they perform in different environments, and what that means for cable design and performance.
What is cable shielding?
Cable shielding is the protective layer, or layers, wrapped around the conductors within a cable. It blocks external electromagnetic interference (EMI) and radio frequency interference (RFI) from disrupting the signals being transmitted through the cable, and it also prevents the cable from interfering with nearby devices or systems.
In simple terms, a shielded cable contains a conductive barrier that protects the signal, while an unshielded cable does not. Making unshielded cables more susceptible to external electrical noise and crosstalk.
What are the different types of cable shielding?
There are four main types of cable shielding: foil cable shielding, braided cable shielding, spiral cable shielding, and combination cable shielding.
1. Foil cable shielding
Foil cable shielding is a thin layer of aluminium or copper bonded to a plastic film and wrapped around the cable conductor. This type of shielding is commonly used in data cables, providing 100% coverage around the conductor, and is often used in high-frequency cables.
Foil shields provide complete coverage but are less flexible, making them ideal for fixed installations or high-frequency applications where strong EMI/RFI shielding is required.
2. Braided cable shielding
Braided cable shielding uses woven copper strands around the conductor in a braided pattern. It is often used in audio cables, video cables, and radio cables at a low- to mid-frequency, valued for its flexibility and strength.
Although it doesn’t provide full coverage, the braid’s overlapping pattern offers excellent mechanical protection and good EMI/RFI performance. Braided shields are also easy to terminate and perform well in applications requiring frequent movement or vibration resistance.
3. Spiral cable shielding
Spiral cable shielding is similar to braided, but instead of being woven, the copper is spiralled around the cable conductor. This type of shielding is most suitable for flexible cables at mid- to low-frequencies.
Spiral shielding typically offers 90–95% coverage and is easier to terminate than a full braid. It’s especially useful for robotic arms, drag chains, or other dynamic systems where continuous flexing is required.
4. Combination cable shielding
Combination cable shielding uses both foil and braided shields – typically copper, or a mix of aluminium and copper. This provides 100% coverage, strength, and flexibility, and is often used in high-performance cables across all frequencies.
By layering foil and braid, combination shields achieve excellent high-frequency noise rejection and mechanical durability, suitable for high-performance data and instrumentation cables.
Foil vs braid shielding
| Feature | Foil Shielding | Braid Shielding |
|---|---|---|
| Typical coverage | 100% | 70–95% |
| Flexibility | Low | High |
| Frequency range | High-frequency | Low- to mid-frequency |
When considering foil vs braid shielding, remember that foil shields offer complete coverage for high-frequency applications. Braids provide superior strength and flexibility for low- to mid-frequency applications.
Overall vs pair shields
In multi-pair cables, shielding can protect each pair individually or all pairs together. An overall shield (OSP) wraps all pairs within one conductive layer, while pair shields enclose each pair separately. Choose overall shielding when broad EMI/RFI protection is required, and pair shielding when minimising crosstalk between individual data pairs is critical – for example, in audio or instrumentation cables.
How does cable shielding work?
Cable shielding creates a barrier that blocks or reflects external electromagnetic interference (EMI) and radio frequency interference (RFI) from penetrating the cable and disrupting transmitted signals. It does this in four ways:
1. Material composition
Cable shields are typically made from conductive metal materials, or a combination of metal and plastic. These materials are chosen for their ability to conduct electricity and their effectiveness at reflecting and absorbing electromagnetic waves.
2. Electromagnetic interference blocking
When EMI or RFI waves contact the shield, the conductive material either reflects the waves away or absorbs them, preventing unwanted signals from reaching the inner conductors.
In short, EMI/RFI shielding diverts or absorbs external electromagnetic energy before it reaches the conductors, helping maintain signal clarity and EMC compliance.
3. Grounding
The cable shielding is usually connected to ground (earth). This grounding provides a path for absorbed or reflected interference to dissipate safely. By grounding the shield, any induced currents or electromagnetic waves are channelled away from the signal conductors and into the ground, where they can do no harm.
Many shielded cables include a drain wire – a bare or tinned copper conductor that runs in contact with the shield. The drain wire provides a low-resistance path to earth and makes termination quicker during assembly. It’s commonly used in data, audio, and instrumentation cables.
4. Containment of emissions
In addition to blocking external interference, cable shielding also prevents the cable from emitting its own electromagnetic signals. This is particularly important in environments with multiple cables and electronic devices, as it reduces the risk of the cable interfering with nearby equipment.
This dual protection – blocking outside noise and containing internal emissions – helps achieve electromagnetic compatibility (EMC) across connected systems.
How to shield a cable
Now that you know what cable shielding is and how it works, how is a cable actually shielded? Shielding is a key part of cable manufacturing, and the process is usually completed in three steps:
Step 1: Check the core construction
The first step of the cable shielding process is checking the core construction.
At this stage, the cable should already contain its conductor or conductors and the core insulation. This must be checked to ensure everything is correct before applying the shield. There are many benefits to wire insulation, so it’s important this is all correct before moving forward.
Inspecting the core ensures that insulation integrity, conductor spacing, and twist ratios meet the performance specifications required before adding any shield.
Step 2: Apply the shielding
The next step is to apply the cable shield. The method depends on which type of shielding the cable requires.
Foil shielding
For foil cable shielding, a layer of aluminium or copper foil is wrapped around the insulated conductors. This foil is often bonded to a polyester film for added strength and durability.
Because foil provides 100% coverage, it’s particularly effective for high-frequency EMI/RFI shielding and is common in signal, data, and instrumentation cables.
Braided shielding
For braided cable shielding, a mesh of copper strands is braided over the insulated conductors. This is usually done using specialised braiding machines.
The braid’s interwoven structure provides mechanical strength and flexibility while maintaining about 70–95% coverage. It’s often used for low- to mid-frequency applications where movement and durability are priorities.
Spiral shielding
For spiral cable shielding, a copper wire is helically wrapped around the insulated conductor, usually by a specialised machine.
Spiral shields are easier to terminate and highly flexible, though less effective at very high frequencies. They’re commonly used in robotics, audio cables, and test leads where flexibility matters most.
Combination shielding
For cables requiring both foil and braid, known as combination cable shielding, the foil layer is applied first and then the copper mesh is braided over the top.
This hybrid approach combines the full coverage of foil with the mechanical resilience of braid, offering all-round protection for multi-environment or high-performance applications.
Step 3: Cover with outer insulation
The final step of the cable shielding process is to cover the shielded cable with an outer jacket.
Known as cable sheathing, jacketing, or cable extrusion, the shielded cable is covered with an outer jacket to provide environmental protection and mechanical strength.
This outer jacket also preserves the effectiveness of the shield by sealing it from moisture, wear, and chemical exposure. Together, the shield and jacket maintain the long-term reliability of the cable’s EMI/RFI protection.
Benefits of cable shielding
Cable shielding provides many advantages, especially in environments where signal integrity is crucial. Here are eight key benefits:
1. Improved signal quality
Cable shielding blocks external electromagnetic fields, preventing them from interfering with the transmitted signal – known as electromagnetic interference (EMI).
A shielded cable minimises EMI and RFI, keeping signals cleaner over distance. This is why EMI/RFI shielding is standard in data centres, industrial networks, and medical electronics.
2. Reduced crosstalk
Cable shielding helps prevent crosstalk, which occurs when signals from adjacent cables affect each other. This is particularly important in densely packed electronic environments.
By reducing crosstalk, shielded cables maintain higher data integrity, which is critical for high-speed transmission. In structured cabling, combining overall and pair shields further reduces crosstalk between twisted pairs, ensuring consistent performance and compliance with EMC standards.
3. Enhanced durability and longevity
The shield adds a physical barrier against damage such as cuts, abrasions, and wear and tear. Shielded cables are also more resistant to moisture, chemicals, and extreme temperatures. This protection helps extend a cable’s lifespan, making it more durable and reliable.
In industrial settings, the outer jacket and shield work together to protect conductors from oil, vibration, and impact – reducing maintenance downtime and extending service life.
4. Compliance with regulations and standards
Many industries have strict regulations regarding EMI and RFI emissions. Using shielded cables helps ensure compliance with these standards and avoids potential legal or operational issues.
Proper cable shielding also reduces the risk of interference that could affect critical systems, enhancing safety in applications such as medical equipment and industrial machinery.
This is particularly relevant under electromagnetic compatibility (EMC) directives, where certified shielded cables play a key role in meeting approval requirements.
5. Versatility in applications
A wide variety of industries depend on shielded cables – from consumer electronics to industrial automation, telecommunications, and medical devices. The range of shielding types (foil, braided, spiral, or combination) allows designers to match flexibility and protection to the application.
In the UK, screened cable is another common term for shielded cable; both terms refer to the same protective function.
6. Performance in high-frequency applications
Shielded cables are especially effective in high-frequency applications, where unshielded cables are more prone to interference and signal degradation. By maintaining signal clarity, shielded cables support high-quality audio, video, and data transmission.
Foil or combination shielding delivers the best high-frequency performance, making it ideal for cables in RF systems, broadcast studios, or medical diagnostics where precision is critical.
7. Reliability in critical systems
Shielded cables provide consistent performance, which is crucial in systems where downtime or signal loss can have serious consequences. Their protection against interference and damage reduces the likelihood of cable failure, minimising downtime and maintenance needs.
By preventing both external interference and internal emissions, shielded cables help maintain continuity in mission-critical sectors such as aerospace, defence, and healthcare.
8. Economic benefits
Although shielded cables may have a higher upfront cost, their durability and reliability often lead to lower maintenance and replacement costs over time.
Reduced interference and signal loss made possible by shielded cables also improve overall system efficiency, potentially saving energy and operational costs. In many industries, investing in shielded cable systems pays off through longer service life, fewer failures, and less recalibration, making them a cost-effective choice for long-term use.
Challenges of cable shielding
While cable shielding offers many benefits, there are also several challenges to consider.
1. Cost
Shielded cables are generally more expensive than unshielded types due to the extra materials and manufacturing steps involved. In large-scale installations, this difference can significantly affect budgets.
However, the long-term value of shielded or screened cables often outweighs the initial cost – especially where interference or downtime would be costly.
2. Complexity in design and installation
Designing shielded cables requires careful selection of the shielding type and thickness, which can complicate production. Installation can also be more complex, as effective grounding must be maintained throughout the system.
Each shielding method – foil, braid, spiral, or combination – affects both flexibility and coverage, so choosing the right design depends on understanding the system’s EMI/RFI environment.
3. Grounding issues
For shielding to be effective, it must be properly grounded. Incorrect grounding can reduce its effectiveness or even increase interference. Requirements vary by application, adding further complexity during installation.
Improper drain wire termination or floating grounds can create ground loops and other noise issues, reducing EMI/RFI performance. Careful earthing and continuity testing are essential.
4. Potential for shield degradation
Over time, shielding materials can degrade due to moisture, chemicals, or mechanical stress. Regular inspection helps keep shielding effective.
Foil shields are more vulnerable to flexing damage, while braids and spirals may corrode if not properly sealed within the outer jacket. Using quality materials and appropriate jacketing extends service life.
5. Electromagnetic compatibility (EMC) issues
Maintaining electromagnetic compatibility (EMC) in complex systems can be challenging, particularly when shielded cables are integrated with other components. Improper grounding can create loops that increase EMI instead of reducing it.
Good EMC design ensures continuous shielding across connectors, cable assemblies, and housings so that every link maintains full effectiveness.
6. Environmental impact
Shielded cables require more material than unshielded ones, which can raise environmental impact. Recycling is also more complex due to mixed metals and plastics.
Sustainability advances – such as recyclable jacketing and halogen-free shields – are helping reduce this impact in modern cable manufacturing.
7. Compatibility with connectors and accessories
Shielded cables often need connectors designed for shield continuity. Ensuring compatibility can add complexity and cost but is vital for performance.
Connectors that clamp or compress the shield maintain full contact, preventing EMI leakage and preserving the integrity of the shielding.
Looking to explore cable shielding for your custom cable needs? Contact our expert team today for more information or find more resources on our blog.