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Does mylar provide a secure seal?

  1. Dec 9, 2014 #1
    I'm using mylar pouches to seal phase change cooling liquid to experiment with cooling in athletic apparel.

    This is an example of the type of 'phase change' liquid im trying to seal: http://www.thewarmingstore.com/tech...edium=GoogleShopping&utm_campaign=SolidCactus

    Im using my own mylar pouches so i can create my own custom shapes.

    So the question: Does mylar provide a secure seal? Meaning the liquid isn't going to seep or evaporate out of it's walls gradually right? I assume since mylar is used for food products, it should be pretty good for this. And yes, the edges are tightly heat sealed so I'm not talking about the liquid seeping out through the edges.

    I think even the phase change liquid (i think its a kind of paraffin?) isn't supposed to be very toxic anyways but i wanted to double check because i will be doing a lot of testing where the pouches need to be in contact with skin for long periods of time.
  2. jcsd
  3. Dec 9, 2014 #2

    Doug Huffman

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    The generic name is Polyethylene terephthalate and the products that I am familiar with are also aluminized.
  4. Dec 9, 2014 #3
    So....aluminized. Does that mean the seal is gonna be good?
  5. Dec 9, 2014 #4


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    You haven't mentioned what sort of pressure is involved. Going by your statements and what little info is offered in the link, I've been thinking that it's just regular atmospheric sea-level. Mylar is pretty good; a lot of off-the-self medicines incorporate it as an anti-tamper/freshness sealant layer inside the lid. The strength is more dependent upon the adhesive than the material. It's very impervious, as evidenced by the fact that it is used in "helium-rated" balloons. (Helium sneaks out between the molecules of things like rubber or elastomers.)
  6. Dec 9, 2014 #5
    Used for helium. Helium known for being leaky. Nice. That's what i was looking for. Thanks Danger.

    It's not going to be used in any abnormal pressured environments. Just hot environments.

    I could also double up on the layers too.
  7. Dec 9, 2014 #6


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    No sweat. You should probably wait for Doug to verify this before rushing out to buy anything, though, since he is the one with experience in the matter. Mine is restricted to the facts that I take a lot of meds and my wife used to work at the Dollar Store and hence blew up a lot of party balloons for customers. :redface:
  8. Dec 15, 2014 #7
    Btw, what is the official scientific word used to describe what I'm trying to get at?

  9. Dec 17, 2014 #8
    Yup i think it's permeability.

    Just read this: "Mylar® polyester film is virtually impermeable to the liquid phase of most chemicals and reagents."

    From here: http://usa.dupontteijinfilms.com/informationcenter/downloads/Chemical_Properties.pdf

    "If you use aluminized Mylar, the helium stays in the balloon for a much longer time, because it does not diffuse through the aluminum coating."

    From here: http://www.newton.dep.anl.gov/askasci/mats05/mats05203.htm

    "Ziplock bags are made of polyethylene (PE) which have an oxygen permeability of 6k - 15k ml O2/(day-mil-sq. meter-atm). Mylar's rating is 50 - 100, several order of magnitudes better. In permeability lower is better. It's not even close, stick with mylar. That and I have doubts about the sealing ability of the "zip" in the ziplock bag."

    http://forum.intherabbithole.com/viewtopic.php?f=15&t=104 [Broken]

    "I for one find it very hard to believe that a dog can smell through mylar, which is a non-permeable membrane (NOTHING can pass through it)."


    Someone legitimize my confirmation bias.
    Last edited by a moderator: May 7, 2017
  10. Dec 18, 2014 #9


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    Permeability refers to an atom (usually gas or volatile atom) being able to pass through a material or membrane. For example, hydrogen is permeable in steels, i.e., it diffuses through steels, usually in atomic form. Once through the steel, it combines into a molecular form, or can form other compounds. Some hydrogen may form metal hydrides.

    Permeability is the property of a material that allows fluids (such as water (liquid) or water vapor (gas)) to diffuse through it, usually into to another medium, without being chemically or physically affected. Water permeates through porous rocks.

    Helium can readily permeate through a number of elastomers. Hence the layer of aluminum on mylar. Aluminum is one of the least permeable metals with respect to hydrogen.

    The other factor is the mechanical seal, the quality of which is usually 'hermeticity'.
  11. Dec 30, 2014 #10
    Thanks, I'll look into this too.
  12. Dec 31, 2014 #11

    Doug Huffman

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    A six inch thick aluminum submarine hull is said to have sweated water at extreme depth until clad with stainless steel
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