Food Storage Part II: Unraveling the Mystique of Mylar Bags

17th March 2012

By Gaye Levy

Guest writer for Wake Up World.

Part 1 can be read here

Today I would like to help unravel the mystique of the Mylar bag.   As with the ubiquitous oxygen absorber, the mention of Mylar bags brings up as many questions as there are answers.   We have all heard that the best way to store dry goods for long term storage is in a Mylar bag but what exactly is a Mylar bag and, more specifically, how are they used?

What is a Mylar bag?

First and foremost, the term “Mylar” is actually one of many trade names for a polyester film called BoPet.   For the technically inclined and the curious, that stands for “Biaxially-oriented polyethylene terephthalate”.   This film was developed by DuPont in the 1950’s and was first used by NASA.

Since then, many uses for Mylar have been embraced due to its high tensile strength and its moisture, light, gas and aroma barrier properties.   Mylar is a also good insulator against electrical disturbances.  For all of these reasons and more, Mylar bags are considered a gold standard when it comes to long term food storage.

Okay. I get it.  What size and thickness do I need?

The two most commonly used sizes for storing food products are the one gallon size (about 10” x 14”) and the five gallon size (about 20” x 30”).

The gallon sized bags are ideal for grains, dried powered foods, spices, hard candy, salts, and other baking ingredients. In addition the gallon bags are useful for protecting valuables including ammo, and medical supplies.   When shopping for gallon sized bags, you should look for a thickness of 3.5 to 4 mil.

The large, 5 gallon sized bag is typically used to line a 5 or 6 gallon plastic bucket.   The bag is filled with product then sealed before closing the bucket up with a lid.   The combination of a Mylar bag inside a plastic bucket makes an unbeatable barrier against the woes and ravages of time, moisture, light and most important, rodents.   The bag alone will not keep out the rodents!   For that you will need a bucket.

Because of the weight of its contents, the thickness of a 5 gallon Mylar bag should be 4.5 mil or more.   And, just so you know, the thicker the bag, the tighter the weave of the polyester – that is what gives it its strength.   As a matter of fact, you will find bags that are 7 mil and even thicker but for most uses, 3.5 mil to 5 mil will work just fine.

Tips for Sealing a Mylar Bag

Sealing a  Mylar bag can be a challenge but with a little practice, you will find the process simple and efficient.   You can use a clothes iron alone, or a with a  FoodSaver and some extra tubing.   But, for an easier and less costly solution, try using use a  hair straightening iron which will only set you back $20 or so.

Here are some other tips:

  • Do not overfill the bag. Remember that your oxygen absorber will suck out the oxygen, leaving only nitrogen in the extra space.
  • Only seal the top inch of your bag. If you need to cut open the bag to remove product, you have the space to seal the bag back up again.   Just don’t forget to add a fresh oxygen absorber.
  • If you are sealing up a powdery substance such as flour, be sure to wipe the inside edges first so that any residual dust is removed.   This will insure a good seal.
  • Check your newly sealed bags a few days after sealing. They should be noticeably compressed. If not, there is a likelihood that the seal was not good or a hole was poked in the Mylar.   Give it another week and if is still is not compressed, cut it open and start over.
  • When sealing pasta or noodles, feel free to seal them in their original packaging. Cut a little hole in the package first, so that the oxygen absorber can do its job in removing every last bit of oxygen, even from the store packaging.
  • Remember, heat is your enemy regardless of the packaging. Store you packaged products below 85 degrees and preferably much lower than that.

What about Vacuum Sealed Bags?

Vacuum seal bags, such as those for the  FoodSaver are a wonderful convenience and easy to use. But alas, they do not have the thickness nor the strength of Mylar bags and the may start to leak after 3 or 4 years. That said, they are still a great alternative for your short-term and mid-term storage items, especially if you are diligent about rotating foods and using them  for your normal meal preparation activities. Just be sure to include an oxygen absorber if you plan to store your vacuum sealed bags for over a year.

Need more information?   Let’s Do Show and Tell!

The following video was put together by a fellow prepper at the  Big Sky Tactical YouTube Channel.   Take a look and if you are so inclined, go to YouTube and subscribe to some of Fletch’s other preparedness related videos.   He’s a great guy – just be sure to let him know that SurvivalWoman at Backdoor Survival sent you!

About the author:

Gaye Levy lives and teaches the principles of a sustainable, self-reliant and stylish lifestyle through emergency preparation and disaster planning. She does this through her website at, an online preparedness blog that provides lifestyle tools, tips, and thoughts to guide you through the back door of life in the 21st century. With an emphasis on prepping and survival, she writes about and shares practical, thoughtful, and inspirational tools for survival in uncertain times.

Backdoor Survival is currently listed on the Survival Top 50. In addition, Gaye is a frequent guest on the Preparedness Radio Network and the soon to be author of a book on 21st century preparedness. Also known as SuvivalWoman, Gaye   speaks her mind and delivers her message with optimism and grace, regardless of mayhem swirling around us.

You can find Gaye through her website at Backdoor Survival, on the Backdoor Survival Page on Facebook, and as Survival Woman on Twitter.

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