# Which is more impermeable **URL:** \ **Category:** Factual Questions\ **Created:** [October 11, 2023, 8:23pm UTC](https://boards.straightdope.com/t/which-is-more-impermeable/991414 "2023-10-11T20:23:53Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Lucas\_Jackson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lucas_jackson/32/303_2.png) [@Lucas\_Jackson](https://boards.straightdope.com/u/Lucas_Jackson)\ **Post date:** [October 11, 2023, 8:23pm UTC](https://boards.straightdope.com/t/which-is-more-impermeable/991414/1 "2023-10-11T20:23:53Z")
Plastic cling wrap or aluminum foil? ---
**Author:** ![Babale](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/babale/32/15666_2.png) [@Babale](https://boards.straightdope.com/u/Babale)\ **Post date:** [October 11, 2023, 8:39pm UTC](https://boards.straightdope.com/t/which-is-more-impermeable/991414/2 "2023-10-11T20:39:48Z")
Impermeable to _what_? The answer will differ if you’re asking about air molecules, visible light, water, etc. ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [October 11, 2023, 8:57pm UTC](https://boards.straightdope.com/t/which-is-more-impermeable/991414/3 "2023-10-11T20:57:10Z")
Per the internet, Aluminium foils thicker than 0.025 mm (0.001 in) are impermeable to light, gases (including oxygen) and water vapor. Foils thinner than this become slightly permeable due to minute pinholes caused by the production process. As for plastic wrap, it depends on the type of plastic it’s made of. Saran wrap used to be made of polyvinylidene chloride, which is about the least permeable plastic wrap. It is now made of low density polyethylene which has a great deal higher gas permeability. Polyvinylidene chloride has an oxygen permeability of 0.6 cm3 μm m−2 d−1 kPa−1 while low density polyethylene under the same conditions has an oxygen permeability of 2000 cm3 μm m−2 d−1 kPa−1, or a factor of over 3,000 times more permeable. So aluminum foil is more impermeable than plastic wraps. ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [October 11, 2023, 9:18pm UTC](https://boards.straightdope.com/t/which-is-more-impermeable/991414/4 "2023-10-11T21:18:21Z")
Regarding impermeability to visible light, I was going to make a joke about transparent aluminum but Googling, there is apparently a [real ceramic](https://en.wikipedia.org/wiki/Aluminium_oxynitride) made of aluminum, oxygen and nitrogen that is transparent. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [October 11, 2023, 9:32pm UTC](https://boards.straightdope.com/t/which-is-more-impermeable/991414/5 "2023-10-11T21:32:27Z")
If you want impermeable plastic then Mylar is very good, and even better if it’s aluminized. ---
**Author:** ![Lucas\_Jackson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lucas_jackson/32/303_2.png) [@Lucas\_Jackson](https://boards.straightdope.com/u/Lucas_Jackson)\ **Post date:** [October 11, 2023, 9:34pm UTC](https://boards.straightdope.com/t/which-is-more-impermeable/991414/6 "2023-10-11T21:34:52Z")
> [@Babale](#): > > Impermeable to _what_? If I wrap a sandwich in each, which will keep it fresher longer? ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [October 11, 2023, 9:50pm UTC](https://boards.straightdope.com/t/which-is-more-impermeable/991414/7 "2023-10-11T21:50:11Z")
Now the question becomes not the impermeability of the wrap, but how air-tight you can make the seals of a 3D package composed of a folded 2D film. I think operator technique will outweigh any inherent difference in the material. With enough effort you can make a water-tight seal in aluminum foil. For casual non-OCD wrapping, I’m going to bet you’ll have better success with plastic cling wrap. I know I would. ---
**Author:** ![jnglmassiv](https://avatars.discourse-cdn.com/v4/letter/j/f07891/32.png) [@jnglmassiv](https://boards.straightdope.com/u/jnglmassiv)\ **Post date:** [October 11, 2023, 9:56pm UTC](https://boards.straightdope.com/t/which-is-more-impermeable/991414/8 "2023-10-11T21:56:14Z")
Rubies and sapphires, too. ---
**Author:** ![Pardel-Lux](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pardel-lux/32/20182_2.png) [@Pardel-Lux](https://boards.straightdope.com/u/Pardel-Lux)\ **Post date:** [October 11, 2023, 10:04pm UTC](https://boards.straightdope.com/t/which-is-more-impermeable/991414/9 "2023-10-11T22:04:40Z")
If wrapping a sandwich is the aim, both aluminium and cling wrap will seal a sandwich well enough if you do it carefully to let it go mouldy before it becomes dry. ---
**Author:** ![Johnny\_Bravo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_bravo/32/493_2.png) [@Johnny\_Bravo](https://boards.straightdope.com/u/Johnny_Bravo)\ **Post date:** [October 11, 2023, 10:38pm UTC](https://boards.straightdope.com/t/which-is-more-impermeable/991414/10 "2023-10-11T22:38:48Z")
Request for nitpicking: Is “more impermeable” correct, or is “less permeable” more accurate? ---
**Author:** ![RitterSport](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rittersport/32/6326_2.png) [@RitterSport](https://boards.straightdope.com/u/RitterSport)\ **Post date:** [October 11, 2023, 10:43pm UTC](https://boards.straightdope.com/t/which-is-more-impermeable/991414/11 "2023-10-11T22:43:36Z")
The correct answer is “which is impermeabler”, of course. The opposite question is “which is permeabler?” Of Saran Wrap and aluminum foil, Saran Wrap is permeablest. ETA: On the question of sealing a sandwich, plastic wrap would do a better job, I bet. ---
**Author:** ![Johnny\_Bravo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_bravo/32/493_2.png) [@Johnny\_Bravo](https://boards.straightdope.com/u/Johnny_Bravo)\ **Post date:** [October 11, 2023, 10:44pm UTC](https://boards.straightdope.com/t/which-is-more-impermeable/991414/12 "2023-10-11T22:44:01Z")
> [@RitterSport](#): > > permeablest. Please don’t bring religion into this. ---
**Author:** ![RitterSport](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rittersport/32/6326_2.png) [@RitterSport](https://boards.straightdope.com/u/RitterSport)\ **Post date:** [October 11, 2023, 10:44pm UTC](https://boards.straightdope.com/t/which-is-more-impermeable/991414/13 "2023-10-11T22:44:56Z")
🙂 (plus letters) ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [October 11, 2023, 10:45pm UTC](https://boards.straightdope.com/t/which-is-more-impermeable/991414/14 "2023-10-11T22:45:05Z")
> [@Johnny\_Bravo](#): > > Is “more impermeable” correct, or is “less permeable” more accurate? And I find smoked salmon sandwiches irresistible. So what happens when an irresistible sandwich meets an impermeable wrapper? ---
**Author:** ![Lucas\_Jackson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lucas_jackson/32/303_2.png) [@Lucas\_Jackson](https://boards.straightdope.com/u/Lucas_Jackson)\ **Post date:** [October 11, 2023, 11:07pm UTC](https://boards.straightdope.com/t/which-is-more-impermeable/991414/15 "2023-10-11T23:07:27Z")
Well, I guess there are more variables than I thought. What started this in my brain was cat food. I often have wet cat food (or tuna) left in the tin, I store it in the fridge - which my wife is not crazy about. I have been storing 1/2 cans in a baggie. But they are only good for about 5 uses before they get grungy. To save, I thought maybe aluminum foil might be better (this is strictly a guess, I haven’t run the numbers). So I used some and she complained about smell. Not sure it had anything to do with the foil as we have lots of potentially smelly things (to her) in the fridge. That’s what made me think of the question in the first place. So… all things being equal (wrapping prowess, etc) which material as it is sold commonly and commercially, would form the better barrier against air and smell transfer? ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [October 11, 2023, 11:14pm UTC](https://boards.straightdope.com/t/which-is-more-impermeable/991414/16 "2023-10-11T23:14:02Z")
The problem with aluminum foil is that it is easy to puncture. Plastic wrap is stretchier, so less so, although something can catch on it. Why not use zip-lock type plastic bags? Those are thicker and therefore less susceptible to nicks and cuts. And the seal is more likely to be airtight than a wrapping, just because people don’t not always get a true tight wrapping in the first place, and even less likely if they open the package more than once. ---
**Author:** ![Lucas\_Jackson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lucas_jackson/32/303_2.png) [@Lucas\_Jackson](https://boards.straightdope.com/u/Lucas_Jackson)\ **Post date:** [October 11, 2023, 11:20pm UTC](https://boards.straightdope.com/t/which-is-more-impermeable/991414/17 "2023-10-11T23:20:33Z")
> [@Exapno\_Mapcase](#): > > Why not use zip-lock type plastic bags? Those are thicker and therefore less susceptible to nicks and cuts. Not a bad suggestion to the ‘storing the cat food’ problem, but like I said, it was this issue that made wonder about the permeability of each material in the first place. However clunky I’ve made it, that’s the question I’ve tried to ask. > [@Lucas\_Jackson](#): > > … all things being equal which material as it is sold commonly and commercially, would form the better barrier against air and smell transfer? ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [October 11, 2023, 11:20pm UTC](https://boards.straightdope.com/t/which-is-more-impermeable/991414/18 "2023-10-11T23:20:53Z")
IMO the _real_ problem with aluminum foil is how you seal all the edges in an airtight fashion. A square or rectangle set atop an open tuna can then folded downwards around / across the sides is wide open to air. A multiply-folded seam of flat unwrinkled foil will be pretty air tight. But will take using WAG 18" x 12" of foil to seal a small tuna can. And result in a large unweildy package. ---
**Author:** ![thorny\_locust](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/thorny_locust/32/431_2.png) [@thorny\_locust](https://boards.straightdope.com/u/thorny_locust)\ **Post date:** [October 11, 2023, 11:22pm UTC](https://boards.straightdope.com/t/which-is-more-impermeable/991414/19 "2023-10-11T23:22:25Z")
> [@Lucas\_Jackson](#): > > I thought. What started this in my brain was cat food. I often have wet cat food (or tuna) left in the tin, I store it in the fridge - which my wife is not crazy about. I have been storing 1/2 cans in a baggie. But they are only good for about 5 uses before they get grungy. They make re-usable caps for the purpose (they’ll fit any can of the size type, not just cat food cans.) I have several of them. [Here’s an example](https://www.chewy.com/ethical-pet-can-covers/dp/56366?utm_source=google-product&utm_medium=cpc&utm_content=Ethical%20Pet&utm_campaign=20207612288&utm_term=&gclid=EAIaIQobChMI3NPq6pDvgQMVj0hHAR0THAyBEAQYBSABEgLTC_D_BwE). – several examples actually, if you scroll down the page. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 11, 2023, 11:23pm UTC](https://boards.straightdope.com/t/which-is-more-impermeable/991414/20 "2023-10-11T23:23:20Z")
> [@Dewey\_Finn](#): > > Regarding impermeability to visible light, I was going to make a joke about transparent aluminum but Googling, there is apparently a [real ceramic](https://en.wikipedia.org/wiki/Aluminium_oxynitride) made of aluminum, oxygen and nitrogen that is transparent. If you’ll accept a compound of aluminum with other elements, it’s even easier: Sapphire is just aluminum oxide. [Next page](https://boards.straightdope.com/t/which-is-more-impermeable/991414.md?page=2)