Using Mylar Bags for Food Storage

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 the gold standard when it comes to long term food storage.

Mylar versus Metalized versus Dry-Pack Pouches

Do not be confused if your vendor of choice uses the term “Metallized Storage Bag” or “Dry-Pack Pouch” instead of Mylar.  This simply means that the bag is not using the Mylar-branded material.  As long as the bag is of food-grade, you are okay. For all intents and purposes, Mylar to a metalized bag is as Kleenex is to facial tissues.

What Size Mylar Bag Should I Use?

The two most commonly used sizes for storing food products are the one gallon size Mylar bag (about 10” x 14”) and the five gallon size (about 20” x 30”).  Various other sizes are available but for starters, these are the two best sizes to have on hand.

The gallon sized bags are ideal for grains, dried powdered foods, spices, hard candy, salts, and other baking ingredients. In addition, gallon bags are useful for protecting valuables including ammo and medical supplies.  When shopping for gallon sized bags, you should look for a minimum 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 first placed inside the bucket and then filled with product.  The bag is sealed before closing the bucket with a tight fitting 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.  The easiest method is to use a hair straightening iron to seal the top of the bag after it is filled with your dry, bulk foods and an oxygen absorber.

I have created a detailed how-to for you in the article How to Seal Food in Mylar Bags.

Here are some additional 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 will 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 closing them up.  They do not have to be brick-like but 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 they 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 longer than a year.

For tips on using a vacuum sealer for food storage, see How to Use a FoodSaver for Vacuum Canning.

Storing Filled Mylar Bags

For long-term storage, it is a good idea to store your filled Mylar bags in buckets or tins.  Why?   Primarily to keep out bugs and rodents that can chew through the Mylar.  Also, as has happened to me, one of my 5 gallon Mylar bags split (accidentally) when I dragged a carton box over it. I had a 40 pound rice mess. It is funny now but it wasn’t at the time.