Same bag specification, two suppliers, prices that differ by half. Most buyers compare price and film thickness first — few compare the one number that decides the product’s fate: the oxygen transmission rate (OTR).

What it governs is concrete: how much oxygen gets into the bag each day — and therefore how long the juice, tomato paste or milk inside stays stable on the shelf. When QC Packaging designs aseptic bag solutions for juice, sauce and dairy customers, OTR is the first number we look at.

1. What OTR measures, and how to read the unit

OTR (Oxygen Transmission Rate) is measured in cm³/(m²·d) — the volume of oxygen passing through one square metre of film per day. The lower the number, the better the barrier.

It is not about leaking. OTR measures how fast oxygen diffuses through the film, not whether the bag is damaged. Spoilage in liquid food runs along two tracks: the microbial track is solved by sterilisation and sealing; the oxidation track is decided almost entirely by OTR. Once oxygen gets in, fat oxidation, pigment degradation, vitamin loss and off-flavours all begin from that point.

2. Same conditions, very different films

A study on the oxygen permeability of aseptic packaging bags published in Packaging Engineering tested common laminates under identical conditions (23°C, 50% RH):

· PET/AL/CPP (foil laminate) 91.8 μm → 0.422 cm³/(m²·d)

· BOPP/AL/PE (foil laminate) 142.5 μm → 0.618

· PET/VMPET/PE (metallised) 144 μm → 6.25

· BOPP/VMPET/PE (metallised) 140.1 μm → 9.40

· BOPP/PE (transparent) 88.7 μm → 45.8

Foil laminates sit more than 100× below transparent film; metallised film is an order of magnitude better than transparent, yet still an order of magnitude away from foil. China’s GB 18454-2001 standard for laminated bags used in aseptic packaging of liquid foods limits foil laminates to OTR < 1.

3. Four relationships that are easy to get wrong

1. Thicker is not proportionally better. OTR falls with thickness as a power function — quickly at first, then flattening out. Material matters far more than thickness: choose the structure first, then the gauge.

2. Material sets the order of magnitude. Foil > metallised > transparent is a difference of orders of magnitude, not of percentages.

3. Temperature cannot be ignored. OTR rises roughly 4-6% for every 10°C increase. Products stored in a South China warehouse or shipped in a summer container are quietly losing shelf life.

4. Humidity barely affects oxygen transmission. Relative humidity has almost no effect on OTR (it affects water-vapour transmission). Moisture-proofing is not an argument for oxygen barrier.

4. How to use the number when choosing a bag

· Start from the product’s oxygen sensitivity. Tomato paste — prone to oxidative browning, where colour grade drives the price — belongs on a foil structure. Products with lower sensitivity, such as plain milk, commonly balance out at metallised laminates. Short-shelf-life chilled products are fine with transparent laminates; over-specifying the barrier is wasted cost.

· Ask for a report, not a claim. Request third-party test data and confirm the test conditions (temperature, humidity, unit).

· Know the test method. The differential-pressure method (GB 1038-2000) is older and less precise; the coulometric/equal-pressure method (GB 19789-2005) is more accurate and can simulate temperature and humidity — it is the mainstream today. Results from the two methods will differ.

· For export and long-distance transport, factor temperature in: a summer sea container runs well above ambient, and OTR rises with it.


FAQ

1. Is a lower OTR always better?

No — it has to match the product. A ultra-low-OTR bag on a short-shelf-life chilled product is over-engineering: you pay for barrier you never use.

2. Can thickness replace a barrier layer?

No. Thickness mainly provides strength, puncture resistance and processing tolerance. The barrier class comes from the material structure; adding gauge to solve oxidation is looking in the wrong place.

3. What is the difference between metallised and foil bags?

Foil is a metal layer; metallised film is a thin vacuum-deposited aluminium coating. They differ by an order of magnitude in OTR (0.42 versus 6.25 in this data set) and in cost — choose by product requirement.

4. How do I verify a supplier’s barrier claim?

Ask for third-party test reports and confirm the method and conditions. The same bag can produce quite different numbers under different test conditions.


QC Packaging has been dedicated to liquid flexible packaging for over twenty years, with our own factory in Wuxi, China. We operate a 100,000-class cleanroom, are ISO 22000 certified, and our products comply with EU 10/2011 and FDA 21 CFR. We serve liquid producers across 12 niche industries — starting from a small order and running the production line with our customers, step by step.

If you are weighing which aseptic bag structure your product actually needs, let’s talk. Start with a small trial batch; we will walk the whole chain with you. That is what “worry-free” means to us.