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.