Mylar bags: construction, barrier, closures and how they get printed

A mylar bag is a laminate: a printable outer film, a barrier layer, and an inner layer that seals. What the bag keeps out — light, oxygen, moisture — comes from that structure, not from how thick it feels in your hand.

That is the single most useful thing to know before buying one, because it reorders the whole decision. Construction and barrier come first. The artwork is built onto whatever dieline those choices produce, not the other way round.

Construction decides shelf presence and most of the cost

• Stand-up pouch. A bottom gusset that folds out so the bag stands up. The dominant retail format, and the best balance of shelf presence, print area and price.
• Flat pouch. Two sealed panels with no gusset. The thinnest and cheapest option. Single servings, samples, sheet goods.
• Side gusset. The traditional coffee silhouette, often paired with a degassing valve.
• Quad seal. Four sealed corners. Strong, squared-off, and good for heavy fills.
• Flat bottom. Five panels and a rectangular base — carton presence with pouch flexibility. The premium look in the category.
• Spouted. A fitment for liquids, gels and refills.

Shelf context matters more than preference here. A flat bottom pouch on a crowded shelf reads as a more expensive product than a stand-up pouch with identical artwork, and a flat pouch reads as a sample even when it is not.

Closures and features

Everything on the bag that is not the bag itself.

• Zipper. Press-to-close is the consumer default. Slider and child-resistant versions exist as certified designs, and that certification is a property of the bag itself rather than something added afterwards.
• Tamper evidence. A tear-off strip, or a sealed header above the zipper that has to be destroyed to open the bag.
• Tear notch. Starts the tear so nobody needs scissors.
• Degassing valve. Lets CO2 out without letting oxygen in. Freshly roasted and fermented products need one.
• Window. Full front, strip or shaped. It trades light protection and barrier for visibility — a deliberate hole in the bag's defences, and worth being deliberate about.
• Hang hole. Round or euro-slot, for peg display.

Material and barrier are not the same thing

This is where buyers most often conflate two separate specifications.

• Thickness is measured in mils, thousandths of an inch. A higher mil means more puncture resistance and a stiffer bag. It does not mean more barrier.
• Foil laminate gives the best barrier and a total light block. Fully opaque.
• Metallised film is lower cost and lighter, near-opaque, and has less barrier than true foil.
• Clear high-barrier structures exist for when the product has to be visible and still protected.
• Barrier is measured as oxygen and moisture transmission rates. Lower is better, and which of the two matters more is decided by your product, not by the bag.

There is a real trade-off underneath all of this: barrier, recyclability and clarity pull against each other. Mono-material structures are the recyclable route, and they currently give up some barrier to get there. Anyone who tells you otherwise is selling one of the three and quietly ignoring the other two.

The three ways artwork gets onto a pouch

These are genuinely different routes, and which one is right depends almost entirely on how many bags you need.

• Labels on stock bags. Buy plain stock pouches and apply a printed label. The lowest entry point by far, the artwork is instantly changeable, and it is the standard route for very small runs and for launching several SKUs at once.
• Digital printed pouches. No plates or cylinders, so there is no tooling cost, artwork changes are free, and several designs can run in one job. The right answer for new brands and seasonal runs.
• Rotogravure. An engraved cylinder per colour. Very high tooling cost that only makes sense at high, stable volume on artwork that is not going to change.

One honest note to save you a disappointing phone call: fully printed pouch minimums are ordered in thousands as an industry norm, and gravure's minimum sits far above digital's. That is not a policy, it is how flexible packaging production works — and it is exactly why the label-on-a-stock-bag route exists and why so many brands launch on it.

What the artwork needs

• The manufacturer's dieline, which comes from whoever is making the bag.
• Bleed.
• CMYK, plus any spot colours called out.
• Barcode placement agreed against the dieline rather than dropped in afterwards.
• White ink specified as its own layer. On clear or metallic film, white is a printed ink and not the absence of one, and leaving it out is the most common way a pouch proof comes back looking transparent where it should be solid.

What you have to supply

The bag is a substrate. The legal content printed on it belongs to the business selling the product.

From you: product identity and net quantity, ingredient or content declarations, your business name and address, country of origin, any warnings your category requires, lot and expiry coding, and the barcodes you own.

If the product is food, the material has to be confirmed food-contact compliant for your intended use and temperature — ask for that in writing, and keep it.

Regulated categories carry their own mandatory labelling, testing and closure requirements, and those vary by jurisdiction. Bring the required content and have it reviewed by someone qualified in your category. The layout is our job. The compliance advice is not, and anyone in a print shop who tells you otherwise is doing you a disservice.

The order to do this in

• First, decide what the product needs kept out, and pick the barrier structure from that.
• Then pick the construction and the closures.
• Then get the dieline from whoever is making the bag.
• Then build the artwork onto that dieline, with white ink and any specials on their own layers.
• Last, proof it, and print.

Doing it in that order costs nothing. Doing it backwards means rebuilding artwork that was drawn to the wrong shape, which is the most predictable avoidable cost in the whole category.

If you are at step one, say what the product is and roughly how many bags you need, and the structure conversation can start there.