Every flexible packaging specification carries two barrier figures. Oxygen transmission rate (OTR) states how much oxygen passes through a given area of film per day. Water vapour transmission rate (WVTR) does the same for moisture. Lower numbers mean a tighter barrier.
Why the test conditions matter
OTR is normally quoted in cc/m²/day and WVTR in g/m²/day, both at a stated temperature and humidity. Comparing values measured under different conditions is a common mistake, because barrier performance changes significantly with humidity, particularly for nylon-based structures. Always check that two quotations reference the same test conditions before concluding one film is better.
Typical ranges by structure
- PET / PE: moderate barrier, suitable for short shelf-life dry goods.
- PET / VMPET / PE: strong barrier at moderate cost, the workhorse for coffee, snacks and pet food.
- PET / AL / PE: highest practical barrier, used for long ambient shelf life and oxygen-critical products.
- Mono-PE with barrier coating: improving, but still behind metallised structures on oxygen.
Matching barrier to product
Fat content, aroma value and target shelf life set the requirement. Roasted coffee and fat-rich pet food oxidise quickly and need a tight oxygen barrier. Crackers and powders fail on moisture first, so WVTR dominates. Products with volatile aromas need barrier in both directions, since aroma loss and off-flavour pickup are the same failure mode.
Confirming it before production
We provide barrier test data for each structure we quote and, when shelf life is critical, run accelerated storage trials with your actual product. Testing the real fill rather than a generic model is the only reliable way to confirm the structure before committing to a print run.