Engineering a paper bag that doesn't break: tensile, TEA and the human grip
Why bag failure is rarely about grammage — and how tensile energy absorption (TEA) predicts real-world handle survival.
Every retailer has the same complaint about paper carrier bags: they fail when wet, they fail at the handle, and they fail when a customer is angry. Solving this is not a question of going heavier. It is a question of understanding three numbers.
Tensile strength is necessary, not sufficient
Tensile measures static breaking force. Real bags fail dynamically — a customer swings the bag, hits a corner against a doorframe, lifts off the counter. Static tensile predicts none of this.
TEA: tensile energy absorption
TEA (ISO 1924-2) measures the energy absorbed before rupture. It is the integral of force × elongation — the area under the stress-strain curve. A paper with high TEA stretches before breaking, absorbing shock loads that would snap a brittle paper.
The TEA targets that actually work
| Bag type | TEA MD (J/m²) | TEA CD (J/m²) |
|---|---|---|
| Light shopping (4 kg) | 60–80 | 120–160 |
| Heavy carrier (8 kg) | 100–140 | 200–260 |
| Cement / industrial sack | 180–250 | 350–450 |
Extensibility is what saves the handle
A paper that elongates 4–6% before break (vs the standard 2–3%) absorbs roughly twice the energy. Extensible kraft (Clupak, sack kraft variants) is the answer for any bag carrying real weight.
"Spec the TEA, not just the tensile. Your customer's frustration lives in the area under the curve."
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