Folding Mylar Bags

There seems to be a good deal of misinformation and lack of information out there about folding of Mylar bags and whether the resulting pinholes will hurt your food storage. I have answered this question before in our FAQ, however because it has come up pretty frequently lately I thought I would do a post about it.

First, I think part of the challenge is because the idea seems to make sense, and so folks read something like ‘folding makes Mylar bags unusable’ and accept the information at face value, understandably. Also, even some of our competitors who should (and probably do) know better do it, for whatever reason.

I think the main cause for the confusion is that folks often use different terms than what they really mean. For example, there is a difference between a pinhole and a puncture when it comes to Mylar bags. A pinhole is a natural part of every Mylar bag. It’s not a dirty word; it doesn’t affect the longevity of your food. Every Mylar bag, whether the lightest 2 mil bag to the heaviest 7.5 mil Mylar bag, has pinholes. There is a measurement that manufacturers use ‘Pinholes per meter squared’ that they use to describe the effect. So when you stick your head into a bag, or shine a flashlight into it, you will see pinholes. That is absolutely normal, and nothing to fear.

A puncture, on the other hand, is an incredibly rare defect in a Mylar bag, usually caused by it being poked by something. It almost never occurs naturally, maybe 1 in 500,000 bags. The main times it occurs is when a manufacturer gets to the end of their roll stock when producing bags, and will occasionally slice a bag. Even though we tell them not to, many times they will tape the tear (which always shocks and annoys me!) and ship them to us. Usually we catch these bags when we package and do not send them out. On a rare occasion, they will make it to a customer, and we apologize when that happens, and will always gladly refund or replace damaged bags.

To understand why pinholes are not an issue, let’s take a look at how Mylar bags are built. Mylar bags are usually composed from 2-5 layers of barriers (though we’ve carried some with 6 on occasion, and for some applications you can get them with more), adhesives and foil. A barrier layer is one that blocks oxygen or moisture, and is usually invisible (except for foil); an adhesive layer is what holds the different layers of the bag together (and some adhesives even have barrier properties as well). And the foil layer is what we actually ‘see’ when we look at the bag, the metal that we refer to as ‘Mylar’. In actuality, Mylar is a clear polyester type material. Only because it is often bonded with an aluminum or metallized layer do we think of Mylar as ‘metallic.’

A pinhole is where the foil layer did not bond to the upper and lower barrier and adhesive layers of the bag, or may happen during shipping. They occur at random places during manufacturing, and again, will show up in all Mylar bags to a greater or lesser extent.  However, every place you see a pinhole, there are still 2-4 layers of material protecting your food.  The very act of storing your food and pulling a vacuum, will cause some more pinholes to occur.  Again, this is completely normal.  As all together those pinholes represent less than 1/1000th or 1/10000th of the total area of the bag, the actual loss of MVTR and OTR is negligible, less than a rounding error.

To demonstrate, I did a Youtube video showing that I can crinkle, crush, and fold a Mylar bag, and it will still be airtight. I took a picture yesterday of a different bag to demonstrate the same thing.  2013-02-23_10-54-13_529It’s hard to tell in the picture, but the bag is holding about a gallon of water with no leaks.

Generally speaking, in our household we only use Mylar bags that have been returned from customers, often because the customer felt folding damaged the bags somehow.  Even after packaging and shipping bags two ways, we have never had a bag fail.  Foil is simply a material that ‘prints’, meaning if you even touch it it will retain the mark.  You can ‘write’ your names on Mylar bags with a coin or fingernail.  Doing this does not hurt the bag.

This business is our livelihood, and I care about our customers.  Many of them have become friends.  I would never do anything to put any of them at risk by shipping product in a way that could potentially make it not work correctly.  We ship hundreds of thousands of bags per month, and there has never been a case where a bag has been returned (except in the case of the tape issue mentioned above) where I have not been able to achieve an airtight seal.  There are several other prepper businesses out there that also ship their bags folded; none of us would even have a business if folding bags damaged them, because we either would have switched to a rolled shipping model, stopped selling them or gone out of business due to the number of returns.

So the next time you are on a prepper or survival forum and someone says you should stick a flashlight in a bag and if it has pinholes it should be returned, please drop me an email, as I will gladly go to the forum and gently reply with the correct information.=)

Keep on prepping folks!

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02 2013

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