Staff · May 2025 · Electronics & EMP
DIY Faraday Bags: Shielding Your Electronics When It Matters Most
Modern survival has a dependency problem. The average prepared person carries a phone with offline maps, a GPS, a handheld radio, a backup battery bank, and possibly a solar charger. That's a meaningful capability stack — and every piece of it is vulnerable to the same threat: a sufficiently powerful electromagnetic pulse.
An EMP event — whether from a high-altitude nuclear detonation, a coronal mass ejection, or a directed electromagnetic weapon — induces voltage surges in conductive materials. Unshielded electronics don't fail gracefully. They fail completely and permanently. The phone with your offline maps, the radio you bought for exactly this scenario, the GPS your navigation plan depends on — all of it, gone, in the same instant.
A Faraday cage or bag is the countermeasure. It is not complicated in principle. In practice, the retail options range from adequate to overpriced, and the DIY versions — built correctly — perform comparably at a fraction of the cost. This guide covers both.
What It Protects Against — and What It Doesn't
Before building anything, be clear about the threat model. A Faraday bag protects against:
- EMP from nuclear detonation — a high-altitude nuclear burst produces a three-phase electromagnetic pulse (E1, E2, E3) that can disable unshielded electronics across hundreds of miles
- Coronal Mass Ejection (CME) — a major solar storm produces the E3-equivalent, capable of inducing damaging current in anything with a conductor, including power lines and unshielded electronics
- RFID skimming — a smaller but practical everyday concern; a Faraday wallet or sleeve prevents contactless card readers from accessing your cards without your knowledge
- Directed EMP devices — increasingly available, increasingly used by sophisticated criminals to disable vehicle electronics and security systems
A Faraday bag does not protect against:
- Physical damage from blast or heat accompanying a nuclear event
- Damage from power surges entering through connected cables — your device must be unplugged and inside the bag
- Radiation — this is shielding for electromagnetic fields, not ionizing radiation
The Physics of Effective Shielding
Not all Faraday bags are equal, and understanding why matters for both evaluating commercial products and building your own. Effective shielding depends on three factors:
Material conductivity. The enclosure must be made of a conductive material. Copper and aluminium are the most effective. Steel is adequate. Metallized fabrics — the material used in most commercial Faraday bags — work but vary significantly in quality. Thin metallized coatings degrade over time and with repeated folding.
Continuity. The shielding must be continuous — no gaps, no seams without conductive contact, no openings. This is where most DIY attempts fail. A bag with a zipper that isn't conductive, or a fold that leaves a gap, has a hole in its shield. Electromagnetic fields are not liquids; they don't need much of an opening to penetrate.
Grounding. Contrary to common belief, a Faraday cage does not need to be grounded to protect its contents from an EMP. Grounding is necessary for some other applications but not this one. An ungrounded, continuous conductive enclosure provides effective shielding.
Commercial Options: What's Worth Buying
If budget allows and you want a tested, ready-made solution, a few products are genuinely worth the money:
Mission Darkness bags are among the most rigorously tested consumer Faraday products. They use a dual-layer TitanRF fabric with laboratory-verified attenuation and conductive velcro closures that maintain continuity at the seal. They're expensive — $30–80 depending on size — but the testing is real.
Silent Pocket makes well-constructed everyday carry options — wallets, phone sleeves, small bags — that work for RFID protection and moderate EMP shielding. Better for daily use than serious EMP prep.
What to avoid: generic "Faraday bags" on Amazon with no attenuation specifications and no independent testing. The metallized film in many of these is too thin to provide meaningful EMP protection and degrades quickly. They may work for RFID. They will not protect your radio from a serious EMP event.
DIY Build: The Nested Enclosure Method
The most effective DIY Faraday container is built on the principle of nested conductive layers with no direct contact between them. Each layer reduces the field that penetrates to the next. Two or three layers of properly built enclosure outperform most commercial single-layer bags.
What you need:
- One or more metal containers with tight-fitting lids — ammunition cans (mil-spec ammo cans with rubber gaskets are ideal), metal trash cans with lids, or metal cookie tins
- Aluminium foil — heavy duty
- Non-conductive padding — foam, cardboard, or bubble wrap
- Conductive copper or aluminium tape with conductive adhesive (not standard foil tape, which has non-conductive adhesive)
The build:
- Line the inside of your metal container with non-conductive foam or cardboard — this prevents your electronics from making direct contact with the conductive walls, which would defeat the shielding
- Wrap each electronic device individually in heavy-duty aluminium foil — minimum two layers, with no exposed gaps. Fold seams carefully and tape with conductive tape
- Place the foil-wrapped devices on the non-conductive padding inside the container
- Seal the lid. On ammo cans, the rubber gasket provides continuity. On other containers, run conductive tape around the seam between lid and body
- For maximum protection, place this entire container inside a second, larger container, again with non-conductive separation between the two
DIY Build: The Faraday Bag Method
For portable protection — items you want to store in a bug-out bag rather than a fixed container — a multi-layer foil bag is the practical option.
What you need:
- Heavy-duty aluminium foil
- Conductive copper tape
- A zip-lock bag or two (non-conductive inner layer)
- Duct tape for the outer layer
The build:
- Place your device in a zip-lock bag — this is your non-conductive inner layer, preventing direct contact with the foil
- Wrap the zip-lock bag completely in two layers of heavy-duty foil, overlapping seams by at least two inches and folding edges tightly. No gaps
- Wrap the entire foil package in a second layer of foil, with seams offset from the first layer — this ensures no gap in the first layer aligns with a gap in the second
- Seal all seams with conductive tape
- Wrap the exterior in duct tape for durability — this also helps prevent the foil layers from developing holes or tears during handling
This build is less elegant than a commercial bag and less protective than a nested ammo can setup, but it is substantially better than nothing and costs under $5 per device protected.
Testing Your Build
A basic functional test costs nothing. Place a phone inside your completed Faraday enclosure and call it from another device. If it rings — or if the caller hears a ring — the enclosure is not providing full shielding. A properly shielded enclosure will send the call immediately to voicemail with no ring, because the signal cannot penetrate to the device.
This test verifies radio frequency shielding, which is a reasonable proxy for EMP shielding. It won't tell you your attenuation in dB, but it tells you whether the enclosure has obvious gaps. If the phone rings, find the gap — usually at the seam or closure — and address it.
Maintenance and Rotation
A Faraday bag is not a set-and-forget solution. Metallized fabric degrades. Foil develops micro-tears. Conductive tape adhesive fails over time. Include your Faraday kit in your quarterly gear audit — unwrap, inspect, re-wrap, and re-test. Rotate the devices inside to ensure batteries are periodically charged. An EMP-protected device with a dead battery is a protected brick.
The electronics inside your kit should also be deliberately chosen for post-EMP utility. A modern smartphone is useful but dependent on infrastructure that may not survive the same event you're protecting against. Alongside it, consider a basic handheld transceiver, a hand-crank or battery AM/FM/shortwave radio, and a USB drive loaded with reference materials — field guides, medical references, maps — that can be accessed on any surviving device.
The threat that makes a Faraday bag necessary is also the threat that eliminates most of the infrastructure your electronics depend on. Build your protected kit around tools that remain useful in that environment — not just tools that survive it.