Do Faraday Bags Actually Protect Against EMP?
Somebody in your life has probably told you that if “the big one” ever goes off, every phone, laptop, and pickup truck in America dies at the same instant. Somebody else has told you faraday bags are snake oil sold to scared people. I’ve spent a lot of hours in spec sheets and shielding test reports, and the honest answer sits between those two camps: a well-made faraday bag very likely would protect a small, unplugged device from an EMP — and the people promising you certainty, in either direction, are selling something.
Let me walk you through the physics, the government report most of the internet quotes without reading, and the difference between a tested bag and a wad of aluminum foil. No bunker required.
How a faraday cage works, in plain English
In 1836, Michael Faraday showed that a conductive enclosure protects whatever’s inside it from external electric fields. When a radio wave — Wi-Fi, cellular, GPS, or the pulse from an EMP — hits a conductive layer, the free electrons in the metal instantly rearrange themselves to cancel the field. The energy spreads across the outside surface and never reaches the interior. Your phone losing bars in an elevator is the accidental version; a faraday bag is the deliberate one, with layers of nickel-and-copper fabric sewn into something that folds shut.
Two details matter more than any brand name. First, the shield needs no power — the physics works on a shelf, in a blackout, forever. Second, the shield only works if it’s complete. A gap at the closure, a torn seam, a cable poking out: each one is a hole in the umbrella. That single fact explains almost every myth I’ll debunk below.
What an EMP actually is — E1, E2, E3 without the drama
A high-altitude nuclear EMP arrives in three waves, and the distinction matters for what you’re protecting. E1 is a spike lasting nanoseconds that couples into circuit boards, antennas, and short cables — it’s the part that threatens your phone and laptop, and it’s too fast for ordinary surge protectors. E2 behaves much like a lightning strike; the EMP Commission called it the easiest component to protect against, because lightning protection already exists everywhere. E3 is a slow surge, lasting seconds to minutes, that pushes damaging currents into long conductors — transmission lines, the big transformers on the grid. E3 is a utility company’s problem, not your backup phone’s. A solar storm, for the record, produces essentially only the E3-style effect, which is why “a solar flare will fry your unplugged laptop” doesn’t hold up.
The source worth naming here is the Commission to Assess the Threat to the United States from Electromagnetic Pulse Attack — the congressional EMP Commission — whose 2008 Critical National Infrastructures report is still the most-cited public research on the topic. One finding cuts through the doom content: the Commission exposed 37 cars and 18 trucks to simulated EMP. Three car engines stopped at roughly 30 kV/m — and restarted. Of the trucks, three stalled and only one needed a tow. Modern electronics are not made of tissue paper. The realistic concern is damage and disruption at scale, not every microchip in the country dying on cue.
So here’s the sober framing: an EMP is a genuine, documented risk to the grid. For your small devices, it’s a plausible risk that a cheap layer of shielding addresses almost entirely. Preparedness is insurance, not fear.
What dB attenuation means for EMP protection
Shielding is measured in decibels of attenuation, and the scale is logarithmic — every 10 dB cuts the energy that gets through by a factor of ten. So:
- 30 dB — one thousandth gets through. Fine for blocking a phone call, thin for EMP.
- 60 dB — one millionth. The floor for serious bags; roughly where certified consumer shielding starts.
- 80 dB — one hundred-millionth. The neighborhood military planners work in for hardened systems.
- 100 dB — one ten-billionth. What the top consumer fabrics claim after lab testing.
Here’s the part marketing pages skip: a dB number with no test behind it is a font choice. What separates a real claim from a printed one is a named standard — MIL-STD-188-125-2, the military standard for shielding against high-altitude EMP, or IEEE 299, the standard method for measuring shielding effectiveness — because a lab either verified the figure or it didn’t. When I ranked bags in my best faraday bag for a laptop guide, verified 80 dB beat asserted 120 dB every single time, and I’d make that trade again.
One more honest caveat, because you deserve it: no consumer product has faced an actual high-altitude nuclear EMP, for the excellent reason that the last US high-altitude test was in 1962 — the Starfish Prime shot, which famously knocked out streetlights in Hawaii from about 900 miles away. Everything since runs on simulators and lab standards. That evidence is strong. It is not a guarantee, and any brand that says “EMP proof” without a footnote has told you something useful about their marketing department.
Aluminum foil, microwave ovens, and chip bags — what actually holds up
Every EMP thread eventually produces the same three DIY heroes. Here’s where each one lands against the physics.
Aluminum foil: works in principle, fails in practice. Foil is genuinely conductive — wrap a phone in three tight layers and it will miss calls, which is a fun kitchen demonstration of Faraday’s cage. The problem is fragility. One pinhole, one loose seam, one corner worn through in a drawer, and the shield leaks — and unlike a sewn bag, you can’t inspect or re-seal a crumpled wrap. Foil is a stopgap for an afternoon, not a plan — though if you want the DIY route done properly, with taped seams and a leak test at the end, I walked through the builds that hold up in how to build a faraday cage.
The microwave oven: a shield tuned to the wrong problem. A microwave’s cage is engineered to contain roughly 2.45 GHz — the single frequency it cooks with. The door seams and vents leak plenty at other frequencies, which is why many phones ring just fine inside a closed microwave. An EMP is a broadband pulse spanning a huge frequency range. Trusting a one-frequency shield against a broadband threat is bringing a rain jacket to a flood. (Also, someone in your house will eventually preheat your backup drive.)
Mylar snack bags: mostly a rumor. The shiny layer inside a chip or popcorn bag is aluminum measured in nanometers, and the fold at the top isn’t a conductive seal. It may weaken a signal; it will not reliably block one. Purpose-built mylar faraday bags with sealed seams exist and test respectably — but they share a name with your pantry trash, not a performance class.
The pattern across all three: the fabric is never the hard part. The seal is. Real bags solve it with two or three shielding layers and a fold-over closure engineered as part of the shield — which is exactly what the lab standards measure.
The realistic reasons to own one (EMP is the bonus)
Here’s my planner’s honesty: if EMP were the only use case, I’d call a faraday bag a low-priority buy for most families. What makes it an easy yes is that the same $30 to $100 of shielding earns its keep on ordinary Tuesdays:
- Privacy and tracking. A bagged phone can’t report location to anyone — useful for travel, custody situations, domestic-violence safety planning, or plain principle.
- Theft that uses radio. Relay attacks copy your car key fob’s signal from inside your house; RFID skimming reads cards. A shielded pouch by the door ends both.
- Digital chain of custody. Police forensics teams bag seized devices so they can’t be remotely wiped — the same logic protects a stolen-then-recovered laptop.
- Grid-down backup. The retired laptop holding your family’s photo archive and document scans sits sealed on a shelf, immune to remote anything — EMP included.
That last one is where I actually live. I’m in tornado alley, where the threat that knocks out my power has a siren, not a warhead — and the same sealed bag covers both without costing me a second thought.
If you’re ready to shop, I’ve done the spec-sheet work already: my Mission Darkness vs GoDark comparison covers the two certified phone-size options head to head, and the laptop faraday bag ranking sorts four full-size bags by verified shielding, honest interior dimensions, and seal design.
Who should get a faraday bag — and who can skip it
Get one if you keep a backup device with irreplaceable data, travel with hardware worth tracking, own a car with keyless entry, or want grid-down insurance that costs less than a tank of gas. Buy a bag with a named standard behind the fabric and run the phone-call test the day it arrives.
Skip it if your only device is the phone in your hand all day. A faraday bag protects what’s inside it, and a daily driver is never inside it. Your first fifty preparedness dollars do more in water storage and a real backup routine — the boring policies come before the exotic ones.
And if someone tries to sell you a bag with the apocalypse instead of a test report, close the tab. The physics is real, the certified products are real, and neither needs the fear to earn a spot on your shelf.
Frequently asked questions
Does aluminum foil work as a faraday cage?
In principle, yes — foil is conductive, and three tight layers with no tears will fail the phone-call test, which is the point. In practice it is fragile: one pinhole or a loose fold leaks signal, and you cannot inspect a wrap the way you inspect a seam. Foil is a weekend stopgap, not a storage plan.
Will an EMP destroy electronics that are unplugged?
Not necessarily — unplugged helps, because a power cord acts like an antenna that feeds the surge inside. But the E1 pulse can still couple directly into a device's own wiring, so unplugged is not the same as protected. Small, self-contained devices fare best; a shielded bag closes the remaining gap.
Is a microwave oven a good faraday cage?
No. A microwave's shielding is engineered to contain one frequency — roughly 2.45 GHz — and the door seams leak everything else. Try it: many phones still ring inside a closed microwave. An EMP is a broadband pulse, so a shield tuned to one frequency band is the wrong tool. A tested bag beats it easily.
How many dB does a faraday bag need for EMP protection?
More is better, and verified beats asserted. Every 10 dB cuts the signal energy by a factor of ten, so 60 dB means about a millionth gets through and 80 dB about a hundred-millionth. Bags whose fabric passed MIL-STD-188-125-2 — the military EMP shielding standard — are the strongest consumer option.
Has any faraday bag been tested against a real nuclear EMP?
No — and be wary of anyone implying otherwise. The last US high-altitude nuclear test was in 1962, so every modern product relies on simulators and lab measurements against standards like MIL-STD-188-125-2 and IEEE 299. That evidence is genuinely good; it just is not a guarantee, and honest brands say so.
Can I test a faraday bag at home?
Yes, in two minutes. Seal your phone inside exactly the way the manufacturer instructs, then call it — it should go straight to voicemail. Follow up by checking that Bluetooth pairing drops and Find My shows the phone offline. That confirms the bag blocks everyday radio signals, which is the testable part of the promise.