Mylar Bags 101: A Plain Language Guide
Everything we wish people knew before buying mylar bags. What they are, how thick they should be, how to store food in them, and how to pick the right one for your product.
What is a mylar bag?
A mylar bag is a pouch made from layers of thin film, usually including polyester and a layer of aluminum, either as foil or as a vapour deposited metallic coating. The metal is what gives most mylar bags their silver inside and their excellent barrier against light, oxygen and moisture.
“Mylar” started as a trade name for BoPET (biaxially oriented polyester) film. It’s a registered trademark of DuPont Teijin Films, but the word stuck the way Kleenex did for tissues. Today people say mylar bag for almost any foil or metallized pouch.
How mylar bags are built
Think of a mylar bag as a sandwich. Each layer has a job:
- Outer layer (often PET): takes the printing and stands up to scuffs.
- Barrier layer (AL foil or VMPET): blocks light, oxygen and moisture.
- Inner layer (PE): melts and seals shut with heat, and is the only layer that touches your product.
Kraft bags swap the outer layer for paper, and clear bags drop the metal entirely. Our custom mylar bags page compares the common structures side by side.
How thick should a mylar bag be?
Thickness is measured in mil (one thousandth of an inch) or microns. One mil is 25.4 microns. Thicker bags resist punctures better and feel more premium, but cost a little more and are stiffer to fill.
| Thickness | In microns | Typical use |
|---|---|---|
| 3 to 3.5 mil | 76 to 89 microns | Samples, sachets and light snacks |
| 4 to 4.5 mil | 102 to 114 microns | Most retail stand up pouches |
| 5 to 5.5 mil | 127 to 140 microns | Coffee, heavier products and premium bags |
| 7 mil and up | 178 microns and up | Long term food storage and bulk bags |
Be careful comparing thickness alone. A thin bag with a real foil layer can outperform a thicker bag without one.
Barrier and shelf life
Packaging people talk about barrier with two numbers. OTR (oxygen transmission rate) measures how much oxygen gets through the film, and MVTR (moisture vapour transmission rate) does the same for water vapour. Lower is better for both.
Foil bags have the lowest OTR and MVTR of any common flexible packaging, which is why they’re used for coffee, cannabis and long term food storage. Metallized bags are close behind. Clear bags let light in and have a much higher OTR, so they suit products that sell quickly.
Shelf life also depends on the product, how it was packed and how it’s stored. Heat, light and a poor seal shorten it. A cool, dark shelf lengthens it.
Mylar bags for food storage
Thick foil mylar bags with oxygen absorbers are a favourite way to store dry food for the long term. Stored well, staples like white rice, wheat and dry beans can keep for decades this way. Here’s the basic method:
- Start with dry food. Rice, wheat, oats, dry beans, sugar and pasta work well. Aim for foods with about 10% moisture or less.
- Fill the bag, leaving about 2 inches (5 cm) at the top for sealing.
- Add the oxygen absorber last, right before you seal. Absorbers start working the moment they hit air, so only open the pack when you’re ready and keep the rest in an airtight jar.
- Press out extra air and seal across the top with an impulse sealer, or a hot clothes iron on a flat board.
- Label the bag with what’s inside and the date, then store it somewhere cool, dark and dry. A food grade bucket protects bags from pests and punctures.
- Check after a day or two. A bag that pulls tight around the food means the absorber did its job.
| Bag size | Holds about | Oxygen absorber |
|---|---|---|
| 7 x 10 in flat bag | 1 L (about 850 g of rice) | 100 cc |
| 10 x 14 in flat bag (1 gallon) | 3.8 L (about 3 kg of rice) | 300 to 400 cc |
| 20 x 30 in flat bag (5 gallon) | 19 L (about 15 kg of rice) | 1,500 to 2,000 cc |
Dry food only
Don’t use oxygen absorbers with moist foods. Moist, low acid food sealed without oxygen can grow the bacteria that cause botulism. If a food isn’t dry enough to snap or crumble, it isn’t a candidate for this method.
Choosing a size
Sizes are written as width x height + gusset. The right one depends on how much space your product takes up, not just its weight. Our mylar bag size guide has an interactive size finder and charts for cannabis, coffee, candy, jerky, tea, powders and food storage.
Are mylar bags smell proof?
A heat sealed foil bag keeps smell in very well, because odour molecules have a hard time getting through metal. The weak points are the seal and the zipper. A good heat seal is close to airtight. A zipper helps a lot after opening, but no reclosable zipper is completely airtight. That’s why CR mylar bags for cannabis combine a sealed tamper strip with a tight zipper.
Recycling and sustainability
Here’s the honest version. Classic mylar bags are several different materials bonded together, which makes them hard to recycle in most Canadian programs. They do use far less material than glass, tins or rigid plastic, and they’re light to ship.
If recycling matters to your brand, there are better options now. Mono material polyethylene pouches can be recycled where flexible plastics are accepted, and compostable kraft pouches suit dry products with a short shelf life. Both trade away some barrier, so they’re not right for everything. Ask us and we’ll tell you straight whether they’ll protect your product.
Glossary
- CR (child resistant)
- Packaging that young children find hard to open but adults can use. Required for cannabis in Canada.
- Dieline
- A template showing where a bag is cut, folded and sealed, plus the safe area for artwork.
- Digital printing
- Printing without plates. Great for short runs and many designs.
- Gusset
- A folded panel that expands when the bag is filled, at the bottom or sides.
- Heat seal
- The strip where layers of film are melted together to close the bag.
- Mil
- One thousandth of an inch, or 25.4 microns. Used to measure film thickness.
- MOQ
- Minimum order quantity. The smallest run a printer will produce.
- MVTR and OTR
- Moisture vapour and oxygen transmission rates. Lower numbers mean a better barrier.
- One way valve
- A small valve that lets gas out of a bag without letting air in. Used for fresh coffee.
- Rotogravure
- Printing with engraved cylinders. Costly to set up, cheap per bag on big runs.
- SKU
- One distinct product, such as one flavour or one size.
- Tear notch
- A small cut at the edge of the seal so the bag tears open cleanly.
- Tin tie
- A bendable metal strip on the bag that folds down to reclose it.
More mylar questions
Don’t see yours? Ask it in the quote form and a real person will answer.
What is the difference between mylar and foil bags?
Most mylar bags contain foil or a metallized layer, so the terms overlap. Strictly speaking, a foil bag has a solid aluminum foil layer, while a metallized bag has a microscopically thin metal coating on polyester. Foil gives the best barrier.
How long does food last in mylar bags?
It depends on the food and storage conditions. Dry staples like white rice, wheat and dry beans sealed with an oxygen absorber and kept cool and dark can last for decades. Foods with more oil or moisture last much less.
Can you vacuum seal mylar bags?
Smooth mylar bags don’t work in most home vacuum sealers, which need textured bags to pull air out. Chamber vacuum sealers do work. For food storage, an oxygen absorber does the same job without a vacuum.
Do mylar bags block light?
Foil and metallized mylar bags are opaque and block nearly all light. Clear bags and bags with windows let light through.
Ready to see pricing?
Send us a few details and we’ll come back with options and real numbers. No pressure and no endless back and forth.