A pouch laminate structure is chosen from what the product needs protecting from (oxygen, moisture, light, aroma, puncture) and for how long. That answer decides which films are combined, in what order and at what thickness, and it is the first thing a converter will ask. This article compares the structures most often used for custom printed stand-up pouches, explains how oxygen and moisture barrier is measured, and shows how to turn a shelf-life target into a barrier brief.
What is a pouch laminate structure?
A pouch laminate structure is the stack of films and layers bonded together to make the pouch wall, written from outside to inside, for example PET/ALU/PE. Each layer has a job: the outer layer carries the print and resists heat during sealing, a barrier layer (if present) blocks oxygen, moisture, light or aroma, and the inner sealant layer forms the seals and touches the product.
A typical three-layer build looks like this:
| Position | Function | Common materials | Typical thickness range |
|---|---|---|---|
| Outer (print) layer | Print carrier, gloss or matt surface, heat resistance, stiffness | PET (often 12 µm), BOPP (often 18-20 µm), paper, MDO-PE, BOPE | Thin films; paper by grammage |
| Middle (barrier) layer | Oxygen, moisture, light and aroma barrier; puncture resistance | Aluminium foil (typically 7-9 µm), metallised PET, PA (nylon), EVOH within a coextrusion, coated films | Very thin for foil and coatings |
| Inner (sealant) layer | Heat sealing, toughness, food contact | LDPE/LLDPE blends, CPP | Thicker; scaled to pouch size and fill weight |
The sealant layer is usually the thickest part of the laminate, and its thickness grows with pouch size and fill weight because it provides much of the pouch's toughness and seal strength. Exact gauges are set at technical review against the product, format and filling equipment.
The layers are joined by adhesive lamination (solventless or solvent-based polyurethane adhesives are common) or extrusion lamination, where molten polymer bonds two webs together. Adhesive laminates need a curing period before slitting and pouch making, which is one reason laminated pouches have longer production routes than single-film bags.
How do the common pouch structures compare?
The common structures differ mainly in oxygen and moisture barrier, appearance and recyclability. Foil gives the highest barrier, metallised PET comes next, transparent coated films and EVOH structures offer high barrier with clarity, and plain PET/PE or BOPP/CPP suit products with modest needs.
| Structure (outside/inside) | Oxygen barrier | Moisture barrier | Light barrier | Clarity / look | Typical applications | Main limitations |
|---|---|---|---|---|---|---|
| PET/PE | Low to moderate | Moderate | None (unless printed white/opaque) | Clear, glossy; windows easy | Short-to-medium shelf-life dry goods, frozen foods, non-food | Not a high barrier; mixed polymers |
| BOPP/CPP | Low | Good | None | Clear or white; crisp feel | Confectionery, bakery, dry snacks with short shelf life | Poor oxygen barrier; narrower sealing window than PE |
| PET/metPET/PE | High | High | High | Metallic, opaque | Coffee, nuts, snacks, pet treats | Barrier drops if the metallised layer cracks under flexing; no windows |
| PET/ALU/PE | Very high when intact | Very high | Total | Opaque, foil look | Long shelf-life coffee, powders, supplements, liquids, sensitive foods | Pinholes and flex cracks reduce performance; no windows; not recyclable in polyolefin streams |
| Kraft paper/PE | Low (paper adds stiffness and look, not barrier) | Low to moderate | Partial | Natural paper | Tea, dry goods with short shelf life | Needs an added barrier layer (metPET, foil or barrier film) for sensitive products; multi-material |
| Kraft paper/metPET/PE or kraft/ALU/PE | High to very high | High to very high | High | Paper outside, barrier inside | Premium coffee, tea, granola | Three materials; windows need a die-cut and patch |
| Mono-PE with EVOH (e.g. MDO-PE or BOPE / PE-EVOH-PE sealant) | High in dry conditions; sensitive to humidity | Good | None unless metallised | Clear to semi-matt | Designed-for-recycling food pouches | Lower heat resistance and stiffness than PET; EVOH share limited by recycling guidelines |
| Mono-PP with AlOx or SiOx coating (coated BOPP / CPP) | Moderate to high | Good | None | Clear | Designed-for-recycling snacks, dry foods, some chilled foods | Thin coatings can crack if over-flexed; sealing window needs care |
| PET/PA/PE | Moderate (PA adds some oxygen barrier) | Moderate | None | Clear | Pet food with hard kibble, sharp or heavy products, frozen foods | PA adds cost; mixed polymers |
Two points that this table cannot show:
- Thickness and grade matter as much as the material name. A thicker or better-metallised film can outperform a nominally "better" structure built cheaply.
- Converted pouches perform worse than flat film. Gusset folds, zipper areas, valve holes and handling all create weak points. Always ask whether barrier data relates to flat laminate or to finished pouches.
What do OTR and WVTR mean?
OTR (oxygen transmission rate) is the volume of oxygen that passes through a square metre of material in 24 hours, usually expressed in cc/m²/day (more fully, cm³/m²·day·atm). WVTR (water vapour transmission rate) is the mass of water vapour passing through a square metre in 24 hours, in g/m²/day. Lower numbers mean better barrier.
Oxygen drives rancidity in nuts and oily snacks, staling and aroma loss in coffee, and colour and vitamin loss in many foods. Moisture drives softening of crisp products, caking of powders and sugar bloom; for moist products, the concern reverses and the pouch must keep moisture in.
Why test conditions decide whether numbers are comparable
Barrier figures are only meaningful when stated with temperature and relative humidity, because both change transmission rates. Typical industry conditions are:
| Measurement | Common test standards | Common test conditions | Why the conditions matter |
|---|---|---|---|
| OTR | ASTM D3985, ISO 15105-2 (coulometric sensor methods) | 23 °C at 0 % RH, or 23 °C at 50 % or higher RH | EVOH and some coatings lose barrier as humidity rises; a dry-condition figure can flatter them |
| WVTR | ASTM F1249, ISO 15106 series | 38 °C at 90 % RH ("tropical") or 23 °C at 85 % RH | Higher temperature increases transmission, so 38 °C/90 % values are typically much higher than 23 °C/85 % values for the same film |
| Whole-package oxygen ingress | ASTM F1307 and similar package methods | Set by test plan | Captures the effect of seals, folds, zippers and valves |
| Flex durability | ASTM F392 (Gelbo flex) followed by barrier or pinhole testing | Defined number of flex cycles | Shows how foil, metallised and coated layers degrade with handling |
When two suppliers quote different OTR figures for "the same" structure, the first check is whether they tested under the same conditions, on the same thickness, and on flat film or finished pouches.
Relative barrier levels
Because published values vary widely by grade and test set-up, most technologists think in bands rather than single numbers. As a working guide:
- Foil laminates sit at the top: when the foil is intact, oxygen and moisture transmission are close to zero. Real-world performance is limited by pinholes and flex cracks.
- Metallised PET and well-made transparent high-barrier films (AlOx, SiOx, EVOH in dry conditions) sit in a high-barrier band, typically one to two orders of magnitude below plain PET.
- Plain PET and PA offer moderate oxygen barrier; plain BOPP and PE offer good moisture barrier but poor oxygen barrier.
- Paper offers essentially no gas or moisture barrier on its own.
Ask your supplier for measured values on the proposed laminate at your agreed conditions, and use those numbers for shelf-life estimates.
How do you turn a shelf-life target into a barrier specification?
Start from how much oxygen or moisture the product can tolerate before it fails your quality criteria, then work back to the maximum transmission the pouch can allow over the shelf life. Food technologists usually set the tolerance from product testing; the pouch arithmetic is straightforward.
An illustrative oxygen calculation, using hypothetical numbers:
- Pouch wall area (both faces plus gusset): 0.06 m²
- Laminate OTR at storage conditions: 1 cc/m²/day
- Daily ingress: 0.06 x 1 = 0.06 cc of oxygen per day
- Over a 180-day shelf life: about 11 cc of oxygen enters the pack
Whether 11 cc is acceptable depends on the product mass and its sensitivity. If testing shows the product can absorb only a fraction of that before going off, you need a lower-OTR structure, an oxygen scavenger, or a shorter shelf life. The same arithmetic applies to moisture with WVTR and the product's moisture tolerance. Real ingress is higher than this flat-film estimate because of seals, zippers and handling, so build in a margin and confirm with real-time or accelerated storage tests on filled pouches.
Nitrogen flushing reduces the oxygen already inside the pack at filling, but it does nothing for oxygen that permeates later. That is why a flushed pouch still needs an appropriate barrier.
Reverse printing and where the ink sits
On clear outer films such as PET and BOPP, the design is usually reverse printed: printed mirror-image on the inner face of the outer film, then laminated. The ink is trapped between the outer film and the adhesive, protected from scuffing and kept away from the food. The outer film supplies the gloss, or a matt film or lacquer supplies a matt finish.
Ink and adhesive choice still matter for food contact, because some substances can migrate through thin layers. For the documents to request, see our food-contact packaging compliance guide. For a comparison of gravure, flexo and digital print on films, see our packaging printing methods guide.
Choosing a structure: decision rules
Use these rules to shortlist structures before discussing them with a converter:
- Very oxygen-sensitive, long ambient shelf life, no window needed: foil laminate, or metallised structure if the shelf life allows.
- Coffee: high oxygen and aroma barrier plus a one-way degassing valve; foil and metallised laminates are established, and high-barrier mono-material structures are increasingly tested (see pouch features for valves).
- Product must be visible: transparent high-barrier film (AlOx/SiOx-coated or EVOH-based), and accept lower light protection.
- Mainly moisture-sensitive (crisps, biscuits, powders): BOPP- or PE-based structures may be enough, with metallisation if shelf life is long.
- Heavy, sharp or hard fills (kibble, hardware): add puncture resistance with PA or a thicker sealant.
- Recyclability target for 2030 onwards: start from mono-PE or mono-PP and add barrier within guideline limits; see recyclable mono-material pouches and the PPWR.
- Natural or craft look: kraft outer, but specify an inner barrier for anything oxygen- or moisture-sensitive.
What to tell a converter about barrier
The more precisely you state the protection need, the less a converter has to guess:
- Product, fill weight and whether it is dry, oily, moist or liquid.
- Target shelf life and storage conditions (ambient, chilled, frozen; humidity of the selling region).
- Known sensitivities: oxygen, moisture, light, aroma, puncture.
- Filling conditions: hot fill, nitrogen flush, freshly roasted coffee, sterilisation or pasteurisation if any.
- Any required test data: OTR and WVTR at stated conditions, on laminate or finished pouches.
- Recyclability target and markets of sale.
- Whether a window, matt finish or paper look is essential.
Bring this list to our custom printed stand-up pouches page or send it through our contact page, and the structure will be proposed and confirmed at technical review.