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Letter: EMP Foil Wrap

Good morning, Hugh and James,

I’ve posed questions before RE: EMP protection [1], and now I have one or two more.

Survival blog had a recent series of posts about how to EMP-proof steel ammo cans; I found them enlightening. but they sparked some questions.

A Faraday Cage

The purpose of a Faraday cage is to completely enclose the item one wishes to protect with a conductive material. This will not permit passage of electromagnetic energy of certain wavelengths. The usual approach to Faraday cages is to exclude all wavelengths of electromagnetic energy. Different electronic components may also be susceptible to energy of different wavelengths. An EMP event may include myriad wavelengths of electromagnetic energy. This creates the preference for solid material, rather than mesh, EMP protection.

I’m wondering why wrapping electronics in sturdy aluminum foil, completely enclosing them in the foil like a well-wrapped Christmas package, would not work. My local restaurant supply house carries heavy duty aluminum foil in 18 inch and 24 inch widths. This foil is slightly thicker ┬áthan foil found in consumer packages.

Less Expensive

It seems to me that “gift wrapping” an electronic device in foil, particularly the cardboard package it came in, which would prevent the device from contacting the foil, making sure no openings of any size are in the foil wrapping, would provide adequate EMP protection. Given that aluminm foil, especially in commercially-sized packages, is quite cheap, the expense to double-wrap, or even triple-wrap, the box is very minimal.

If a layer (or two) of aluminum foil is adequate, placing the foil-wrapped device in a steel ammo can would provide protection against the foil wrapping being damaged; the ammo can would not have to have exhaustive EMP-protective measures performed on it to ensure EMP protection of devices inside it.

Am I way off base here and missing something important, or is this something that everyone else is ignoring? – NK

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#1 Comment By WILDBILL On July 27, 2017 @ 10:32 am

I place the items to be protected in cardboard or some other insulating material then wrap with three layers of aluminum foil and hopefully that will protect them.

#2 Comment By Bob On July 27, 2017 @ 11:48 am

I’ve been double-wrapping all of my electronics for years. I just figured the aluminum foil didn’t protect against all of the frequencies possible, so I put the most expensive/essential items in ammo cans and live with the risk to the rest of it.
I am very interested in what the more knowledgeable among us have to say on the matter.

#3 Comment By Dario Monje On July 27, 2017 @ 11:54 am

I have heard that micro-waves are “Farraday cages. Does anybody know for sure. One thing that is certain, they are designed to keep electronic waves inside them. I’d like to know. There must be millions of discarded worn out micro-waves around. Maybe we can make use of them?

#4 Comment By Garry On July 27, 2017 @ 12:02 pm

As far as using microwave ovens as a faraday cage, I just put my cell phone in our microwave and called it from my wife’s phone. The call went through.

#5 Comment By Benjammin On July 27, 2017 @ 12:34 pm

Not quite right. We use perforated sheets for faraday cages (similar to the shielding on microwaves) to break up eddy currents, which defeat the ability of the solid sheet material to shunt energy, and make it become transparent to AC emf at various frequencies/energy levels. Also, to be truly effective, a faraday cage needs to be coupled electrically to ground, so the energy has somewhere to go. Without this coupling, the material can electrically saturate (as with the plates of a capacitor developing reactance) and once again becomes transparent to emf. Just wrapping something in a conductive material won’t necessarily be an effective barrier to an EMP. It may offer a modicum of transient protection under certain conditions. Wouldn’t you rather be sure your equipment will survive?

#6 Comment By Nosmo On July 27, 2017 @ 1:49 pm

I understand the benefit of perforated material in creation of a Faraday cage; I have not been able to locate suitable perforated material at reasonable cost.

It is my understanding that perforation size and spacing are related to a shielding material’s effectiveness in protecting from EMP, and that different frequencies of radiated energy will require different perforation sizes and spacings.

Is there any reason that perforated foil would not meet those rquirements? I recognize that material thickness affects shielding, but I can’t find any data on that.

On a related issue to Tom (below); I suspect by placing Visqueen – an insulator – between conductive layers you are building a capacitor.

#7 Comment By Tom On July 27, 2017 @ 1:11 pm

I gift wrapped my most sensitive items. 1. I would take the items preferably first in a non-conductive box such as cardboard. 2. I’d then wrap it in several layers of the heaviest plastic visqueen I could find. This provides a heavy non-conductive covering and also prevents sharp corners from puncturing the foil. 3. THen I bought rolls of bubble wrap insulation that has aluminum foil on both sides. I wrapped the item in this bubble wrap and then used aluminum tape (from Walmart) to seal the edges. I then repeated this with another layer of visqueen and bubble wrap. Finally one last heavy layer of visqueen to protect the bubble wrap from puncture. Then storing them in a cardboard box to move around is one layer of protection. Therefore, these items have 1. non-conductive box, visqueen, double sided foil bubble wrap, visqeen, double sided bubble wrap and one more layer of visqueen. This seem liked the most cost effective way to protect electronics. I even wrapped up new Honda 2000EUI generators like this.

#8 Comment By Matt in Oklahoma On July 27, 2017 @ 1:36 pm

Like Garry stated wrap you cell phone in whatever you choose and then call it. This is kind of a litmus test and you will see many failure of many types of “protection” including store bought ones.
Before I get jumped on by everyone about how it’s not a scientific method but a common sense approach that if it won’t stop calls it won’t stop EMPs.

#9 Comment By Travis Riley On July 27, 2017 @ 1:43 pm

I wrap the original box in fmoil, plastic, foil, plastic, foil, plastic. Three layers. It is the only thing I have found to defeat a cell phone signal. Then the package goes into a steel or aluminum container. Microwave ovens alone offer little, if any, protection.

#10 Comment By anonymous On July 27, 2017 @ 2:15 pm

I often wonder if the EMP saved devices like radios and cell phones will do any good. If the sending devices are not protected sufficiently, a good radio would not have any signal to detect. Just wondering!

#11 Comment By JD On July 27, 2017 @ 8:08 pm

Many HAM operators around the globe unwrap their radios and start talking after the EMP.

#12 Comment By Ian Worrall On July 27, 2017 @ 2:49 pm

A couple questions I have on this. I’m a newbie to prepping so forgive me if the questions sound stupid.

1. If your electronics are all wrapped up how do you use them?

2. If you are using your electronics when an EMP goes off are you going to have time to stick them in the faraday cage?

3. If the EMP knocks out the power grid and you don’t have electricity, how are you going to run them? This is assuming you don’t have solar power. And even if you do have solar power to run your electronics, the main grid probably doesn’t so how would you access the internet on your computer?

#13 Comment By JD On July 27, 2017 @ 8:11 pm

1) You don’t. Many folks purchase duplicate items and store them. HAM radios, wind up radios, etc.
2)No, again duplicates are usually stored IMO.
3)Batteries, wind up, solar, etc. No more internet for a while. The best outcome IMO will be all the HAM operators that start talking.

#14 Comment By Phelps On July 27, 2017 @ 3:02 pm

Foil works. It’s what an actual electrical engineer who works at NASA recommends.


As for microwaves, yes, they are faraday cages for microwave frequencies only. The cage is designed to keep you from being cooked by microwaves, and isn’t designed for other frequencies. Go with the aluminum foil.

There’s a lot of overkill on this site when it comes to EMP that reminds me more of voodoo “if I work harder at it I’ll get better results” that just isn’t supported by science.

#15 Comment By JR On July 27, 2017 @ 3:03 pm

Dr. ARthur Bradley, PhD has a channel on YouTube called DisasterPreparer. He has several videos on EMP and faraday cages, but here are the most relevant. He uses aluminum foil much like the author suggests in addition to other layers.



#16 Comment By David Martin On July 27, 2017 @ 4:04 pm

Dave of Oregon
A good EMP shield with foil can be achieved, but like what was mentioned above having a layer of plastic insulator, and another layer of foil will just make a capacitor. It will become resonant somewhere in the electromagnetic spectrum and pass energy. If there is an EMP, OR CME broadband pulse, then it stands to reason it will pass some energy at some frequency during the pulse. A single layer. Preferably grounded will be your best protection. There is a very good video on Aamron that relates to this subject quite well. I am an old Army radio teletype operator, our shelter box for the radio station was a fully shielded box with mesh door shielding on the doors, and any through put for power or wire line communications was not only shielded but filtered with special filters. the only thing that was not shielded was the antenna pass through, but, if given enough time to prepare for a nuke attack, our proceedure was to disconnect all cables from the box/rig and place the metal connector cover cap over the entrance connectors. Huh! At one time I was told not to educate my men about EMP, because it was a CLASSIFIED subject. I just explained that we all had crypto clearances and we DEFINATELY had a great need to know. Another thought, be sure all metal foil inside and outside is bonded to each other, even if you place like a foam insulator between layers, bond inside to outside, to reduce any capacitive action ocuring.
I would even recommend protecting solar cells, if not in use. They are PN junctions, just like any other solid state device. It’s better safe than sorry. I know there is conflicting arguments on the subject of solar panels, but you be the judge. You may even want to purchase a few extra sets of Diodes for you generators and protect them also. Think of an extention cord running to your generator as an antenna. Energy could build up from an EMP/CME and fracture the junctions of your diodes. thus your generator will be dead. I even keep a spare charge controller, and inverter squirriled away in my EMP can. Blessing to all Dave

#17 Comment By Phelps On July 27, 2017 @ 4:43 pm

The ground was necessary because you had signal and power passthroughs. For cached gear, the ground is at best useless and at worst a tail that allows charges to build up. A pure faraday cage does not ground out the charge — the entire electrical grid faults to ground, and it’s where the EMP voltage builds the worst. It relies on skin effect, not grounding, and grounding interferes with the skin effect.

(Don’t confuse grounding with electrically tying everything together. The whole cage has to be electrically connected to itself but it doesn’t need to be or gain any benefit from being grounded if there aren’t pass throughs.)

#18 Comment By KB On July 27, 2017 @ 5:58 pm

With all the heavy wrapping of these products I would be concerned about moisture condensation on sensitive electronic parts.

#19 Comment By Charles K. On July 27, 2017 @ 6:45 pm

Just a note: don’t confuse grounding and bonding. I would suggest getting the latest in National Electrical Code books. They come out every 3 years, the latest being 2017. This will help with all your electrical work. For the current discussion, grounding and bonding, and when to use either or both.

#20 Comment By Old spook On July 27, 2017 @ 7:13 pm

Ammo can inside a larger ammo can WORKS well, or so I’m told by people that know about such things . no special seals or gaskets just can in a can . if I tell you more I’ll have to kill you

#21 Comment By Don Williams On July 28, 2017 @ 1:19 am

1) Strangely enough I was at Costco today and noticed that they have military style Ammo cans on sale — a 30 caliber can nested inside a 50 caliber can. Cost is $14. They are new but seem identical to the military surplus — metal thickness, weight, all steel, rubber gaskets, etc. Maker is Heritage Security Products. Seems a weird thing for Costco to be selling to suburbanites.

2) Re shielding, the energy of EMP is almost all in frequencies below 100 MHZ. See page 48 of

#22 Comment By William T. Prepperdoc On July 28, 2017 @ 2:33 am

I wrote an entire book on this topic, with scores of references, many of them scholarly. I dont have the test gear that some of my references own, but I was able to learn from their knowledge and experiments.
Radio waves are tricky to understand; after 45 years of ham radio and 2 degrees in E.E., I’m still learning. Several of the letters above are on track, others not so much. First: EMP and CME are quite different; CME poses no significant risk other than through wild swings of powerline voltage and eventual grid damage/failure. EMP’s E3 wave has the CME risk, while the E1 wave (a nanoseconds-long pulse of immense electromagnetic field, roughly 25 kV/meter at peak) is what may damage any semiconductor device with more than several inches of wire connected to it that isn’t significantly protected. Tube gear in tests conducted many years ago appeared FAR more impervious….tho protection is still advisable. One writer hits the nail on the head above: if you have to keep your gear in Faraday cages forever, how are you ever going to use it? {there may be more than ONE attack, right?} Second: Please forget “ground”. this is a waste of time, folks. Faraday cages do not “fill up” or “become transparent”; their protection is based on Maxwell’s laws which indicate extreme difficulty in maintaining an electrical field INSIDE a conductor. Third: The known spectrum of the RF waves coming from an EMP tails off after 100 MHz and goes off a cliff after 1 GHz, so this is mainly the SAME PROBLEM THAT DIGTAL HAMS HAVE TO DEAL WITH: how to protect against RFI. Only, this is RFI of enormous magnitude that can not only reset electronics, but FRY THEM in nanoseconds. In the book that I labored long to write, I explain a lot more, but basically you want gas discharge surge arresters (easily purchased, about $2) on all antennas longer than a few inches and you want antennas that are NOT broadband. Finally, for the Faraday Cages you do not need (nor can you easily obtain) infinite protection. You merely need to reduce the E field around your precious stored gear to a survivable range. If you live very near a very strong cell tower (probably +40 to +50 dBm ) you may find it very difficult to shield a cell phone (sensitivity -100 dBm) sufficiently [150 dB] to prevent a received call. Yet you may still have provided very good EMP protection. No one knows for CERTAIN because we only have simulations — not nuke bomb tests! Aluminum foil is NOT a solid perfect conductor so it cannot fully exploit the protection of Maxwell’s law, but it is better than nothing! Yes, if you have nested (insulated) foil enclosures, there will certainly be capacitance between them, but this is an electromagnetic problem, not a series tuned filter problem…..the outer foil will tend to greatly reduce the spatial E field, and the next inner foil will reduce it further, and so on. It would be a great PhD thesis requiring a LOT of computer time to prove exactly what is best (or a very lucky experimenter). By merely compacting their cords, and removing extraneous wires from important objects you greatly reduce their vulnerability; then place inside a good conductive closed surface (with only SMALL holes if any), and if you like, repeat! Microwave ovens must have a waveguide for desired 2.4 GHz energy to enter, you might want to cover that entrance port…. Otherwise they may provide 40-80 dB of protection at various frequencies. Remember: vacuum tube gear (think, HEATHKIT) actually survived emp simulation attacks WITHOUT A SCRATCH WHILE OPERATING. That might give you some good ideas. I’ve seen demos where laptops (WITHOUT WIRES Going to thEM!!!) survived EMP simulations. The key is to get rid of those wires, or else have well-engineered gas arrestors on any important wires…..get a EE to work on it for you, or an Extra Class ham who has read what I and others have written. Hope this helps….. sincerely,

#23 Comment By Don Williams On July 28, 2017 @ 12:33 pm

Thanks for the point about the waveguide into the microwave. I was puzzled by a commenter’s report that a cell phone works inside the oven since cell phones generally work at roughly the same frequency band as microwaves — 1.8 and 2.1 Ghz vs 2.45 gigahertz.

#24 Comment By MHL On July 28, 2017 @ 3:12 pm

I’ve turned an old 1958-ish vintage refrigerator into a Faraday cage. I lined the inside with discarded foam gym mats & have sealed any openings that had been to channel electric/coolant/etc and around the door gasket with 2 layers of foil tape. It works like a charm….my cell phone doesn’t pick up a signal when placed inside & the door is resealed. Since the previous homeowners left the fridge behind & the gym was happy to have me take the mats my only expense is the tape!