Faraday Zone

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How Faraday cages work

A Faraday cage is a conductive enclosure that is closed. Bags, pouches, tents, and rooms are all cages if the material and the seams complete the circuit. An open zipper is not a cage.

Updated August 20, 2026

The enclosure, not the brand

Michael Faraday showed that a conducting shell rearranges charge so the interior is shielded from external static fields. For radio, the same idea holds when the enclosure is complete at the frequencies you care about: walls, seams, and the opening.

Faraday Zone sells and reviews products as portable cages. We do not treat a silver undershirt as the same object as a Mission Darkness evidence bag. Clothing can reduce exposure at the body. It does not isolate a phone.

Why openings leak

Slots and gaps behave like antennas. A Faraday bag that is 99% closed can still pass a cellular handshake. That is why Faraday Zone talks about closures as much as fabric: magnetic folds, roll-tops, Velcro, and zippers fail in different ways.

Windows are a designed opening. A transparent panel is useful in forensics and is a different leak budget than a solid wall. Window and non-window bags should never share one score.

Attenuation is a curve, not a slogan

Blocking is measured in decibels across frequency. A number without a band is incomplete. 80 dB at 900 MHz and a leak at 5 GHz Wi-Fi are different products for different jobs.

IEEE 299 is a common enclosure method. MIL-STD-188-125 is cited on EMP-oriented bags. Faraday Zone will name the standard, the lab, and the date when we cite a test — including our own.

What a cage cannot do

It cannot hide a device that is outside it. It cannot stop a camera that is already recording locally unless you also control power and microphones as a separate problem. It cannot turn a phone bag into a shielded room.

A key fob pouch is a tiny cage for relay theft. A TitanRF kit is material for a cage you still have to build. A HAVN cap is apparel.

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