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.
Table for Quick-Chooser Mini
Grains that are fine, like rice and flour: Go a little higher; particles trap more air between them.
- Coarse foods like pasta and beans can have a little less CC.
- If you’re not sure, round up. It’s better to go a little too far than not far enough.
What Foods Keep Best in Mylar?
- Dry Staples (less than 10% moisture)
- Foods with little oil and moisture are the best candidates:
- Wheat berries, white rice, rolled oats, and barley
- Lentils, split peas, and dry beans
- Semolina, dry corn, popcorn, and pasta
Vegetables and fruits that have been dried out (really dry), powdered milk that doesn’t have any fat, and baking mixes that don’t have any fat
- Foods to Stay Away From (Risk of Botulism and Quality Problems)
- Don’t eat wet or greasy foods in Mylar that doesn’t have oxygen:
- Brown rice, whole wheat flour, nut flours, and granola with oils
- Fresh or soft foods, wet pet food, and jerky that isn’t completely dry
- Anything that has more than 10% moisture
In places with little oxygen, these can go bad or grow harmful bacteria. Put it in the fridge, freezer, or another method if it’s oily or wet.
More than just food: spices, seeds, and more
Mylar is great for spices, herbal teas, and garden seeds (as long as they stay cool). You can also pack medical supplies like bandages and gauze to keep them clean and dry. Just don’t seal anything that needs air to breathe or has special storage needs.
How to Pack a Mylar Bag in Steps
Get Ready and Set Up
Get your gear together: Mylar bags (5–7 mil), OAs (still sealed), a scale or measuring scoop, a marker, a heat sealer or iron/hair straightener, a flat board, and a clean bucket or bin.
Set up your workflow: Before you fill the bag, write down the food, weight, date, and OA size.
Sanitation: Make sure everything is clean and dry. No greasy surfaces or wet hands.
Methods for heat sealing (iron, hair straightener, impulse sealer)
Iron for the home: Set it to cotton or linen and press it along a board or a wooden ruler wrapped in parchment for a clean edge.
Hair straightener: Surprisingly good for making tight, even seals.
Impulse sealer: If you store things often, it’s the easiest and most reliable way to do it. Set the temperature for the thickness of your bag and do a test strip.
Protecting Your Mylar with Buckets, Bins, and Backups
What Makes 5-Gallon Buckets and Gamma Lids So Popular?
A 5-gallon food-grade bucket keeps the Mylar safe from rodents, sunlight, and holes. Gamma lids that screw on make it easy to open and close without having to pry. The bucket protects you, and the Mylar keeps the oxygen out.
- Storage, Stacking, and Labeling Conditions
- Cool, dark, and dry, with a temperature range of 10–21°C (50–70°F). Heat shortens shelf life.
Stack safely: Don’t stack too high, and move older stock to the front (FIFO: First In, First Out).
Make sure the labels are clear. They should include the type of food, the net weight, the pack date, the OA size, and any cooking ratios.
- Checking for quality and fixing problems
- Checking a seal and making sure it absorbs oxygen
- The seal should be smooth, shiny, and free of wrinkles. Gently pull on both sides.
Absorption: The bag may feel firmer after 12 to 48 hours. You might have a leak or an OA that is too small if it still looks like a balloon.
Puffy bags, pinholes, and do-overs
A bag that is puffy? If you need to, reseal a fresh edge with a new OA.
Pinholes: These are usually caused by sharp grains or rough handling. Don’t cram; use buckets instead.
Leaky corners: To be safe, double-seal or add a second narrow seal below the first.
Safety Notes You Should Read
No-Go: Moist Foods + Oxygen Absorbers
Botulism can grow in places where there is little oxygen and a lot of moisture. That’s why we only keep dry foods in Mylar with OAs. If you’re not sure how much moisture is in the air, don’t take the chance—use refrigeration, freezing, or another safe method.
- Temperature, mice, and cross-contamination
- Every 10°C (18°F) increase can cut shelf life in half. Stay cool.
Rodents: Buckets stop them from chewing, but Mylar alone won’t.
Cross-contamination: Don’t use bags that smelled bad with delicate foods again (spices can ghost!). Use clean scoops and containers.
Price Ranges and Tips for Buying
Bags: Depending on their size and thickness, they should cost between $0.20 and $2.00.
OAs: When you buy them in bulk, they cost very little per bag, usually just a few cents to a few dollars.
Kits: Starter kits come with bags, OAs, and sometimes labels, which is great for beginners.
When and how to use again
You can carefully cut above the seal, empty it, and then seal it again lower down. Look for pinholes, creases, and smells. If the bag is damaged, stop using it for non-essential things like dry goods for a short time.
Camping gear, medical supplies, and documents
Mylar is great for keeping things dry and blocking light. Things like first-aid kits, matches, and emergency blankets come to mind. You can also keep important papers safe (use a sleeve to keep the ink from getting on them) and meals for camping trips that are already portioned out.
Warning about electronics (ESD Awareness)
Anti-static or ESD shielding bags are not the same as standard Mylar bags. Use the right ESD-safe bags for electronics like hard drives and boards. Mylar can keep dust and moisture out, but it won’t stop static electricity from getting through.
Mylar and Other Options
Bags for Vacuum Sealing
Good for storing things in the freezer and for short- to medium-term storage. But over time, they let more oxygen through. Mylar + OA wins for a shelf life of decades at room temperature.
Lids and jars for canning
Great for small batches, being able to see what’s in the pantry, and keeping rodents out. Disadvantages: they can break, are heavy, and let light through unless they are kept in the dark.
Food-Grade Buckets That Don’t Have Mylar
It’s better than nothing, but buckets alone don’t have low oxygen. Putting Mylar on the inside of buckets gives you both a barrier and armor.
Common Mistakes and Myths
More oxygen absorbers are always better
For dry foods, using too many OAs isn’t usually dangerous, but it wastes money and can change the shape of the packaging. Make sure your OAs are the right size for the amount of food and the type of food.
Double-Bagging Fixes Everything
Two bad seals don’t make a good one. Double-bagging can help keep things from getting punctured, but the most important things are the quality of the seal and the right size of the OA.
Any dry food is safe
“Dry” to the touch doesn’t mean it has low moisture. Even with OAs, oily grains, nut flours, and foods high in fat still go bad. Know what you’re eating.
Quick Starter Kit and Plan for the First Hour
List of Things to Buy
- A mix of quart and 1–5 gallon Mylar bags (5–7 mil)
- Oxygen absorbers (100 to 3,000 cc sets)
- Five-gallon buckets with gamma lids that are safe for food
- Permanent marker, measuring scoop, and kitchen scale
- An iron, hair straightener, or impulse sealer can be used to heat things up.
- Labels, parchment paper, and a flat board
60-Minute Walkthrough
10 minutes: Put labels on the bags with the date, weight, and OA size.
10 minutes: Set up the station and only open OA when you’re ready.
25 minutes: Fill the bags, add OA, and seal them with heat.
5 min: Put the bags that are sealed into buckets and snap the lids shut.
10 minutes: Write down your inventory in a notebook or spreadsheet and keep it in a cool, dark place.
- More Advanced Advice
- Nitrogen Flushing (Optional, When It Works)
You can flush the headspace before sealing if you have nitrogen. This pushes oxygen out of the way and makes your OAs work less hard. It’s helpful for big bags or delicate foods that you don’t want to be compressed.
Drying agents vs oxygen absorbers
- Desiccants don’t take away oxygen; they take away moisture.
- Oxygen absorbers don’t take away moisture; they take away oxygen.
Use OAs for long-term shelf life and desiccants for crunchy foods like crackers. You might use both in some cases, but only with foods that are really dry.
In conclusion
If you use the right kinds of foods, mylar bags are a simple, cheap, and proven way to keep them fresh and make them last longer. Put them in buckets, seal them well, and store them in a cool, dark place with the right-sized oxygen absorbers. If you do that, you’ll turn everyday staples into a pantry you can count on for a long time, whether you’re preparing meals, saving money, or getting ready for an emergency. Start with small steps, learn the technique, and then grow with confidence.
Questions and Answers
1) How long can food stay fresh in Mylar bags with oxygen absorbers?
If you store them correctly (in a cool, dark, and dry place), white rice, wheat, and beans can last for 10 to 30 years. Expect several years when the temperature and dryness are right for herbs, powdered milk, and dehydrated foods.
2) Do Mylar bags need to look like they are sealed to work?
No. Not all low oxygen looks like a brick wrapped in plastic. A bag that is a little soft can still be perfect if it has a good seal and the right OA size.
3) Is it okay to put Mylar bags in the freezer?
Yes, but that’s too much. Vacuum sealer bags work great in freezers. Mylar is great for long-term storage at room temperature.
4) What thickness is best for beginners?
5–7 mil is the best thickness for durability and easy sealing with common tools.
5) Can you use oxygen absorbers more than once?
No. Once they are out in the open and used up, they are done. Put any OAs you don’t use in a small, airtight jar to keep them fresh until you need them again.