RF Gasket Types: Finger Stock, Knitted Wire and Conductive Elastomer
How the RF gaskets used in shielded doors and panel joints work, their advantages, and which one to choose in which situation.
3 min readOctober 9, 2026
Air In, Signals Out
People and equipment work inside a shielded room, so fresh air and cooling are essential. But an ordinary vent cut into the wall is a window signals can pass through easily. The larger the opening, the greater the leakage.
The part that solves this dilemma is the honeycomb filter. This honeycomb-like metal grille lets air through with almost no resistance while stopping radio-frequency signals.
The Waveguide Principle
Each cell in a honeycomb filter behaves like a small metal tube. In physics this structure is called a waveguide, and every waveguide has a cutoff frequency. Signals below that frequency can't pass through the tube and weaken rapidly as they travel.
The smaller the cell diameter and the longer the cell depth, the greater the attenuation. That's why rooms targeting high dB at high frequencies use finer, deeper honeycombs.
What to Consider When Choosing
The first criterion is the room's target frequency range and dB level. The second is airflow: the filter area must be large enough to pass the air the HVAC system needs with low pressure loss. The third is how the filter is mounted in the wall.
The joint between the filter frame and the wall panel must be sealed with a conductive gasket. Even the best honeycomb is useless with poor mounting. These points are checked separately during the acceptance measurement.
Maintenance and Cleaning
Honeycomb cells collect dust over time. This doesn't reduce shielding performance, but it reduces airflow and strains the air conditioning. That's why a removable dust filter in front of the honeycomb is recommended.
During annual maintenance visits, the honeycomb surface is cleaned and the frame gasket is checked. That preserves both comfort and signal isolation.
Frequently Asked Questions
Does a honeycomb filter block sound?
No, honeycomb filters provide no acoustic insulation. In TEMPEST rooms that need it, silencers are added to the ducts.
Can the AC unit be placed inside the room?
It can, but the piping to the outdoor unit and the power line must also pass through filtered penetrations. In most projects air is supplied from outside through ducts.
What is a honeycomb filter made of?
Usually brass, steel or aluminum, coated against corrosion.
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