What are Mylar bags made of?
Mylar Bags are made from a special type of stretched polyester film called BoPET (biaxially oriented polyethylene terephthalate). This material is created by stretching polyethylene terephthalate (PET) in two directions, which makes it very strong, lightweight, and resistant to gases, light, and moisture.
To make them more effective for storage and packaging, Mylar bags often have multiple layers:
- Polyester (PET): Provides strength, durability, and flexibility.
- Aluminum foil layer: Acts as a barrier against light, oxygen, and moisture.
- Polyethylene (PE) inner layer: Allows the bag to be heat-sealed for airtight storage.
This layered structure is what makes Mylar bags ideal for long-term food storage, smell-proof packaging, and product protection.
Mylar, "Foil," and Regular Plastic
A lot of the time, "foil bags" have a layer of metal on them, but they might not be the same quality or thickness as Mylar.
- Normal plastic, like zip bags, lets oxygen in, so it's okay for a short time but not for decades.
- Mylar bags are strong, block light, and let very little oxygen through, especially when used with oxygen absorbers.
Why Mylar Bags Are Important
Light, oxygen, moisture, and pests are the enemies of freshness.
Light, oxygen, and moisture can all break down food. Pests are the extra bad guys. Mylar's light barrier and low oxygen permeability, along with a good seal, slow down the process of deterioration by a lot. This keeps bugs out and keeps the flavor, color, nutrition, and texture of the food.
Shelf-Life Gains in the Real World
Mylar bags can keep white rice, wheat, oats, and beans shelf-stable for 10 to 30 years if you use the right oxygen absorbers and store them in a cool place. Herbs and spices keep their smell much better, and dried foods stay tasty instead of becoming bland and stale.
- Different Types and Thickness Choices
- What Mil Ratings Mean (3.5–7+ mil)
A "mil" is one thousandth of an inch. 5–7 mil Mylar is the best thickness for long-term storage because it is flexible enough to seal easily and thick enough to keep pinholes from forming. For smaller bags or short-term use, 3.5 to 4 mil works. 7+ mil is very strong, but it's harder to heat-seal with regular tools.
Clear vs. Opaque, Gusseted vs. Flat
Opaque (metallized) blocks light the best, so it's the best choice for storing food for a long time.Clear-front "window" bags are great for displaying items in a store, but they let light in. Keep them in a dark bin.
- Gusseted bags are easier to fill and stay upright.
- Flat bags are great for small amounts, spices, and refills that you use every day.
- Sizes that are common (1 quart to 5 gallons)
1 quart or less: nuts, spices, jerky, seeds.
1–2 Gallon: This is the right size for medium batches of grains, pasta, and dehydrated meals.
Oxygen Absorbers: The Perfect Pair with Mylar
How Oxygen Absorbers Do Their Job
Oxygen absorbers (OAs) have iron in them that rusts on purpose. This binds oxygen and makes the air inside low in oxygen. Less oxygen means slower oxidation, fewer bugs, and a longer shelf life.
Picking the Right CC Size
"CC" tells you how much oxygen an absorber can hold. For dry foods, the volume of the bag plus the headspace should equal the total CCs. Some common picks are
1-quart bag: 100 to 300 cc
1-Gallon bag: 300–500 cc
A 5-gallon liner holds 2,000 to 3,000 cc, which is usually several packets that add up to that amount.
