Obviously, low, medium and high, are relative terms. Here in the Pacific Bag world, a high barrier bag is a bag with aluminum foil because aluminum foil has the best barrier properties of all the flexible packaging materials available. If a customer wants the best protection and longest shelf life, we recommend aluminum foil.
On the low end of our world is polyethylene. This is the plastic people may be familiar with from grocery bags or bread bags. Polyethylene does provide some protection against moisture and oxygen, especially compared to paper bags or cardboard cartons, but compared to aluminum foil, polyethylene allows several hundred thousand times more oxygen through it than aluminum foil does. Therefore, we call polyethylene “low” barrier. Between aluminum foil and polyethylene are a variety of products, most notably metallized polyester. Since these are between the high and the low end in our world, we call them medium barrier.
If you have any questions or would like to discuss this further, please feel free to either call us at (800) 562-2247 or email us at firstname.lastname@example.org.