# self inflating envelopes **URL:** \ **Category:** Factual Questions\ **Created:** [July 16, 2002, 2:22pm UTC](https://boards.straightdope.com/t/self-inflating-envelopes/119237 "2002-07-16T14:22:06Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![scm1001](https://avatars.discourse-cdn.com/v4/letter/s/c4cdca/32.png) [@scm1001](https://boards.straightdope.com/u/scm1001)\ **Post date:** [July 16, 2002, 2:22pm UTC](https://boards.straightdope.com/t/self-inflating-envelopes/119237/1 "2002-07-16T14:22:06Z")
just packed my camera away for repair in an large parcel envelope. After piercing it a couple of times it inflated to protect the camera. Any ideas how it does this? I tried googling but came up a fat zero. ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [July 16, 2002, 2:25pm UTC](https://boards.straightdope.com/t/self-inflating-envelopes/119237/2 "2002-07-16T14:25:44Z")
Do you just pierce it wherever you want or is there a “pierce here” indication? ---
**Author:** ![scm1001](https://avatars.discourse-cdn.com/v4/letter/s/c4cdca/32.png) [@scm1001](https://boards.straightdope.com/u/scm1001)\ **Post date:** [July 16, 2002, 2:28pm UTC](https://boards.straightdope.com/t/self-inflating-envelopes/119237/3 "2002-07-16T14:28:28Z")
There is a pierce here instruction ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [July 16, 2002, 2:33pm UTC](https://boards.straightdope.com/t/self-inflating-envelopes/119237/4 "2002-07-16T14:33:27Z")
Good. My WAG wouldn’t accomodate the other option. 😉 In piercing, you expose an agent to a reagent, which results in a chemical reaction which fills the bag with gas. Sorry I can’t be more specific, but it’s just a WAG. WAG quotient of this answer: 82.7% ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [July 16, 2002, 2:40pm UTC](https://boards.straightdope.com/t/self-inflating-envelopes/119237/5 "2002-07-16T14:40:00Z")
Here is _my_ WAG: If you take some cotton or some other padding material, put it in a plastic bag and pump out the air, the padding will get compressed and almost flat. If you then poke a hole to let some air in, it will expand again. I think it’s the same principle. They sell bags that work this way to store clothes. You put your winter clothes, blankets, futons, etc. in a big plastic bag and hook up a little pump. The bag shrinks to about 1/3 of the size, taking up less space in the closet. I don’t know if people actually use it, but they show it on infomercials in Japan all the time. ---
**Author:** ![stuyguy](https://avatars.discourse-cdn.com/v4/letter/s/ec9cab/32.png) [@stuyguy](https://boards.straightdope.com/u/stuyguy)\ **Post date:** [July 16, 2002, 2:43pm UTC](https://boards.straightdope.com/t/self-inflating-envelopes/119237/6 "2002-07-16T14:43:35Z")
It’s simple. The walls of the envelope contain foam rubber that has been compressed flat and sealed inside an airless, airtight bladder. The foam rubber naturally wants to expand to its full size/shape but cannot do so because air cannot enter the bladder. By puncturing the bladder you are letting the air in. The walls of the envelope inflate as the foam expands. ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [July 16, 2002, 2:44pm UTC](https://boards.straightdope.com/t/self-inflating-envelopes/119237/7 "2002-07-16T14:44:55Z")
Oh, wait. The envelope is _padded_? That was mentioned before. ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [July 16, 2002, 2:46pm UTC](https://boards.straightdope.com/t/self-inflating-envelopes/119237/8 "2002-07-16T14:46:26Z")
So why is the “pierce here” instruction necessary? ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [July 16, 2002, 2:47pm UTC](https://boards.straightdope.com/t/self-inflating-envelopes/119237/9 "2002-07-16T14:47:02Z")
I meant to say _wasn’t_, of course. :rolleyes: ---
**Author:** ![scm1001](https://avatars.discourse-cdn.com/v4/letter/s/c4cdca/32.png) [@scm1001](https://boards.straightdope.com/u/scm1001)\ **Post date:** [July 16, 2002, 4:29pm UTC](https://boards.straightdope.com/t/self-inflating-envelopes/119237/10 "2002-07-16T16:29:48Z")
> [@](#): > > \*Originally posted by stuyguy \* > \*\*It’s simple. The walls of the envelope contain foam rubber that has been compressed flat and sealed inside an airless, airtight bladder. The foam rubber naturally wants to expand to its full size/shape but cannot do so because air cannot enter the bladder. By puncturing the bladder you are letting the air in. The walls of the envelope inflate as the foam expands. \*\* I think you are probably right. I will take one of these apart tonite - but a casual inspection shows no obvious sign of a chemical or other blowing agent. Very cunning these envelope people ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [July 16, 2002, 4:36pm UTC](https://boards.straightdope.com/t/self-inflating-envelopes/119237/11 "2002-07-16T16:36:40Z")
Please let us know what you find, **scm1001** , as there are several unanswered questions here. Also, please inspect carefully for a patent number or manufacturer name. I’d love to look up the patent info on this. ---
**Author:** ![scm1001](https://avatars.discourse-cdn.com/v4/letter/s/c4cdca/32.png) [@scm1001](https://boards.straightdope.com/u/scm1001)\ **Post date:** [July 17, 2002, 9:31am UTC](https://boards.straightdope.com/t/self-inflating-envelopes/119237/12 "2002-07-17T09:31:51Z")
Dear Kneadto know the envelop is indeed vacuum powered, by Xpander Pak ([www.xpander.com](http://www.xpander.com)) patents nos (US and foreign) 4,193,499 and 4,620,633 I should have guessed the vacuum bit, but my mind was thinking too high tech, with little gas cylinders etc ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [July 17, 2002, 12:24pm UTC](https://boards.straightdope.com/t/self-inflating-envelopes/119237/13 "2002-07-17T12:24:50Z")
:shakes fist: You’ve won this round, **scr4** and **stuyguy** , but _I’ll be back!!!_ :husky gentlemen in white uniforms haul **Knead** away: