# How can one block radio waves? **URL:** \ **Category:** Factual Questions\ **Created:** [November 2, 2002, 12:04am UTC](https://boards.straightdope.com/t/how-can-one-block-radio-waves/134918 "2002-11-02T00:04:41Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![Binarydrone](https://avatars.discourse-cdn.com/v4/letter/b/3da27b/32.png) [@Binarydrone](https://boards.straightdope.com/u/Binarydrone)\ **Post date:** [November 2, 2002, 12:04am UTC](https://boards.straightdope.com/t/how-can-one-block-radio-waves/134918/1 "2002-11-02T00:04:41Z")
OK, I know that this is going to spawn tinfoil hat type jokes, so first let me offer a disclaimer that this information is for a short story that I am writing! What I am wondering is this: What material when made into a helmet or when used to line a room would stop a wide range of radio waves? ---
**Author:** ![UncleBill](https://avatars.discourse-cdn.com/v4/letter/u/d26b3c/32.png) [@UncleBill](https://boards.straightdope.com/u/UncleBill)\ **Post date:** [November 2, 2002, 12:23am UTC](https://boards.straightdope.com/t/how-can-one-block-radio-waves/134918/2 "2002-11-02T00:23:07Z")
[Water?](http://newton.dep.anl.gov/askasci/phy99/phy99245.htm) [url=http://www.cellphonesar.com/research/rf\_radiation/shielding\_rf\_hazards/faraday\_cage.htm]Faraday Cage?\*\* ---
**Author:** ![UncleBill](https://avatars.discourse-cdn.com/v4/letter/u/d26b3c/32.png) [@UncleBill](https://boards.straightdope.com/u/UncleBill)\ **Post date:** [November 2, 2002, 12:24am UTC](https://boards.straightdope.com/t/how-can-one-block-radio-waves/134918/3 "2002-11-02T00:24:22Z")
Oops. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [November 2, 2002, 12:47am UTC](https://boards.straightdope.com/t/how-can-one-block-radio-waves/134918/4 "2002-11-02T00:47:23Z")
Any continous metal grounded surface should work ---
**Author:** ![RadioWave](https://avatars.discourse-cdn.com/v4/letter/r/91b2a8/32.png) [@RadioWave](https://boards.straightdope.com/u/RadioWave)\ **Post date:** [November 2, 2002, 12:51am UTC](https://boards.straightdope.com/t/how-can-one-block-radio-waves/134918/5 "2002-11-02T00:51:00Z")
I’ll try not to take this personally… How about a [mesh screen](http://web.haystack.mit.edu/RET/Atmospheric/radio1.htm)? [Copper](http://www.copper.org/cutopics/Ct78/RFI.html) would also do a good job of disrupting EM waves. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [November 2, 2002, 1:11am UTC](https://boards.straightdope.com/t/how-can-one-block-radio-waves/134918/6 "2002-11-02T01:11:30Z")
> [@](#): > > \*Originally posted by k2dave \* > \*\*Any continous metal grounded surface should work \*\* It can have holes in it as long as the holes are smaller than the wavelength of the radio wave you are trying to block. Your microwave door is a good example. The holes are small enough to block the radio waves but big enough to let light through. Do a web search on “Faraday cage.” Should give you lots of info. ---
**Author:** ![TheLoadedDog](https://avatars.discourse-cdn.com/v4/letter/t/35a633/32.png) [@TheLoadedDog](https://boards.straightdope.com/u/TheLoadedDog)\ **Post date:** [November 2, 2002, 5:01am UTC](https://boards.straightdope.com/t/how-can-one-block-radio-waves/134918/7 "2002-11-02T05:01:42Z")
Wasn’t there a controversy in the UK a couple of years back regarding bus companies wanting to line the bus windows with a film designed to block mobile telephone transmissions? ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [November 2, 2002, 5:44am UTC](https://boards.straightdope.com/t/how-can-one-block-radio-waves/134918/8 "2002-11-02T05:44:06Z")
I’m sure lead would do nicely. ---
**Author:** ![Boyo\_Jim](https://avatars.discourse-cdn.com/v4/letter/b/87869e/32.png) [@Boyo\_Jim](https://boards.straightdope.com/u/Boyo_Jim)\ **Post date:** [November 2, 2002, 7:12am UTC](https://boards.straightdope.com/t/how-can-one-block-radio-waves/134918/9 "2002-11-02T07:12:16Z")
Regardless of the material, a _hat_ doesn’t work, as you need total enclosure for protection. Above, to the sides, and below. So you have to go with some kind of coverall, space suit thingee woven of metallic fiber. Or some kind of vehicle that you remain inside for protection. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [November 2, 2002, 7:42am UTC](https://boards.straightdope.com/t/how-can-one-block-radio-waves/134918/10 "2002-11-02T07:42:41Z")
You can either reflect them away from you with a conducting surface or you can put an absorbing material between you and the transmitter. As was mentioned by **yojimboguy** , to make sure, you need to be totally enclosed because reflections cause the waves to come at you from all directions. If you are out in space this isn’t a problem, but if there are relective surfaces around the waves come at you from a lot of directions. I would go with a reflecting shield. Absorbing shields have to be pretty thick to handle low frequencies. ---
**Author:** ![DougC](https://avatars.discourse-cdn.com/v4/letter/d/7feea3/32.png) [@DougC](https://boards.straightdope.com/u/DougC)\ **Post date:** [November 2, 2002, 10:45am UTC](https://boards.straightdope.com/t/how-can-one-block-radio-waves/134918/11 "2002-11-02T10:45:47Z")
- - - Powdered iron will work pretty well, and can be mixed into many ordinary paints. I saw a story a while back about a company that was going to make panels like this for lining the insides of movie theaters, to keep people’s cell phones from ringing. ~ ---
**Author:** ![Urban\_Ranger](https://avatars.discourse-cdn.com/v4/letter/u/e9c0ed/32.png) [@Urban\_Ranger](https://boards.straightdope.com/u/Urban_Ranger)\ **Post date:** [November 2, 2002, 2:29pm UTC](https://boards.straightdope.com/t/how-can-one-block-radio-waves/134918/12 "2002-11-02T14:29:35Z")
As mentioned above, a Faraday cage. ---
**Author:** ![Rayne\_Man](https://avatars.discourse-cdn.com/v4/letter/r/df705f/32.png) [@Rayne\_Man](https://boards.straightdope.com/u/Rayne_Man)\ **Post date:** [November 2, 2002, 3:29pm UTC](https://boards.straightdope.com/t/how-can-one-block-radio-waves/134918/13 "2002-11-02T15:29:09Z")
> [@](#): > > \*Originally posted by TheLoadedDog \* > \*\*Wasn’t there a controversy in the UK a couple of years back regarding bus companies wanting to line the bus windows with a film designed to block mobile telephone transmissions? \*\* Some train companies do this on one or more carriages so that fellow passengers are not disturbed by mobile phones. On the same subject Virgin have just launched a new generation of trains. One of the selling points was to try to pursuade businessmen to leave their cars at home and use the train with the promise of having an office on wheels. Unfortunatly the windows of these trains have been coated with a metalic substance to cut down glare. It also stops radio waves and so these business men cannot use their mobile phones. They are not pleased !