In our article on metalized packaging, we explained one of the most important concepts in barrier packaging: flat sheet barrier is not the same as real-world package barrier. Datasheets are measured on pristine, unconverted film. Real packages get structured, folded, sealed, shipped, stocked, and gripped.
This time, we measured the difference — with coffee packaging bought straight off the shelf.
Why Oxygen Barrier Matters So Much for Coffee
Roasted coffee is one of the most oxygen-sensitive products in flexible packaging. Oxidation degrades aromatics and turns fresh coffee stale — and once it starts, there’s no reversing it. That’s why premium coffee packaging is built around high-barrier laminations, one-way degassing valves, and hermetic seals. If the film’s oxygen barrier fails, everything else is irrelevant.
The Two Structures We Tested
The long-standing gold standard for coffee is a PET / aluminium foil / PET / LDPE lamination. The challenger is a PET / MetPET / LDPE structure, which serves as an application as barrier performance “on par with foil.”
How We Tested
We purchased consumer-ready coffee packaging directly from the market — no lab-made samples — and measured oxygen transmission rate (OTR) per ASTM F1927 (100% oxygen, 23°C, 48h, detection limit 0.05 cc/m²/day).
Then we subjected samples to controlled flex handling at three severity levels — light, medium, and heavy (1.5 and 10 final rotations) — to simulate the pinholes, flex cracks, and metallization fractures that real packages accumulate between the packing line and the consumer’s kitchen.
The Results
Three findings stand out:
Even undamaged MetPET isn’t equivalent to foil. Every unhandled foil sample measured below our instrument’s detection limit of 0.05 cc/m²/day. Unhandled MetPET averaged roughly 0.07 — measurable oxygen transmission, right out of the gate, at least 40× higher than foil’s worst case.
MetPET degrades fast under handling. Light handling alone pushed MetPET to 2–7 cc/m²/day. Heavy handling reached 10. Foil, by contrast, stayed below the detection limit through light and most medium handling.
Heavily abused foil still beats lightly handled MetPET. Even our worst-case foil samples (12–21 cc/m²/day after heavy flexing) outperformed MetPET samples that had been only lightly handled — and were roughly an order of magnitude better than heavily handled MetPET.
What This Means for Coffee Brands
If your product’s shelf life depends on keeping oxygen out — and for coffee, it does — the data is clear. Foil-based laminates remain the secure, low-risk performance benchmark. You should be cautious, but rather than fearing and always replacing a valuable option, use it for the right area.
MetPET has its place, and for less oxygen-sensitive products it can be a smart, cost-effective choice. But for coffee, “on par with foil” doesn’t hold up under testing — especially once handling enters the picture.
Learn More About Packaging Materials
Choosing the right barrier structure starts with understanding how materials perform beyond the datasheet. Explore our Packaging Materials Guide series to learn more about the materials, structures, and design considerations used in flexible packaging today — or reach out for the full study and sample-level data.
Testing performed per ASTM F1927, with methodology and raw data available on request.
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