FAQS: Mylar Bags & Oxygen Absorbers

There are a few myths and misconceptions about Oxygen Absorbers and Mylar Bags and here are some answers for domestic use.  

No. The “vacuum-packed look” is NOT an indication that the oxygen has been removed. This myth is probably why many people seem to think some oxygen absorbers do not work. Just because all the air has NOT been removed from the bag does NOT mean that all the oxygen has not been removed. Air is made up of many gases and Oxygen Absorbers do not absorb air; they absorb oxygen, which is 21% of air. That means roughly 1/5 of the air volume will be gone but 4/5 of the air remains no matter how many oxygen absorbers are used.  Other than filling up, oxygen absorbers have the ability to work indefinitely. If left 'out in the open air' there's no protection and they will absorb immediately, but there is a curve: they start slow and pick up speed. 10 minutes of handling time is recommended, but actually you can leave them out for around an hour before they no longer absorb their full rating. Oxygen absorbers do NOT suck up the air like a vacuum.

Yes. This is a feature of the Mylar foil. Mylar is one of the toughest flexible materials ever created constructed of 3 or more layers, laminated together. Mylar is a transparent and flexible polyethylene plastic (both LLDPE and Mylar are forms of polyethylene) with high tensile strength that is biaxially-oriented (a grid-like structure used for remarkable strength).  These components have some great oxygen protection properties which comes from the mylar layer. The third layer is the layer of foil which provides most of the extreme oxygen and moisture protection. While mylar is flexible, metal foil is not and therefore the so-called "holes" you see are simply cracks in the foil layer and these cracks will not affect the performance of these mylar bags. If unsure, fill the bag with water as a test. 

No. Mylar is transparent and metal has been added to the Mylar to increase its barrier properties. People in the past have wondered if light is going to damage their food and it is true that all forms of energy have some potential to effect matter.   What is true is that direct sunlight can have a noticeable effect, however, inside a metalised bag in a cool, dark storage place, there is virtually no effect from light. PackFresh gallon and quart Mylar Bags are metalised through a process called vapor deposition where aluminium is sprayed onto the Mylar surface to make it a better oxygen barrier. When you hold these bags to the light, you can still see through them but they still provide an excellent barrier and will keep food preserved for well over 25 years. Mylar Bags are nonporous, impermeable to gas, reflects light, flexible, durable and puncture-resistant, easy to use and affordable. 

Mylar® brand is a registered trademark owned by Dupont Tejjin Films for a specific family of plastic sheet products made from the resin Polyethylene Terephthalate (PET). The true generic terms for this material are either polyester film, polyester sheets or plastic sheet. The metalised coating over the PET sheet provides a barrier which is what gives Mylar bags the ability to protect food inside the bag from its surrounding conditions. 

No, not for PackFresh USA Mylar Bags. Mylar bags manufactured by PackFresh USA are made of food-grade, non-toxic Mylar. The metal coating on PackFresh Mylar Bags is NOT on the inside of the bag, instead the material used inside of the bag is the same material used in vacuum sealer food bags which are non-toxic and food-safe. The only thing to bear in mind is that the bag can get very hot to touch and caution should be used when adding boiling water to the Mylar Bag. If you are wanting to add boiling water to the bag then you should purchase a gusseted bag like the Mylar Food Grade 7 Mil Bag or the 64oz (2 Quart) Mylar 5 Mil Food Grade Bag. The 64oz (2 Quart) 5 Mil Mylar Bag is said to be the ideal bag for reconstituting food on-the-go – it can hold a decent sized meal and you can add boiling water. However, it would be advised to place the bag in a sturdy container to hold it up when adding boiling water. 

PackFresh USA manufacture and supply Mylar Bags to many companies who produce dehydrated and freeze dried food for backpackers, campers and hikers, food that is intended to be conveniently rehydrated with boiling water in such bags.  

NOTE: Please be aware that adding boiling water to some bags is NOT recommended as they may not be made of high quality Mylar and, in fact, may be of poor quality plastic. The quality of Mylar Bags vary from manufacturer to manufacturer and it is advised to check with the manufacturer if or not you can add boiling water to your Mylar Bag. As stated here, you can do this with PackFresh Mylar Bags because they are made out of food-grade and non-toxic material.