Tensile strength (paper)
Tensile strength is the maximum stretching force a paper or board can withstand before breaking, measured in machine direction and cross direction. It is reported as kN/m or as breaking length in metres.
Paper has two distinct tensile values because its fibres orient predominantly along the machine direction (MD) — the direction the web travelled through the paper machine. MD tensile is consistently higher than cross-direction (CD) tensile, often by a factor of two or three.
Tensile is tested per TAPPI T 494. A strip of paper of standard width is clamped at both ends and pulled apart at a constant rate; the force at break is the tensile strength.
Where tensile matters: paper bag durability (a kraft sack needs both MD and CD tensile to withstand handling), web breaks on a printing press (low MD tensile breaks the web), label and tag stocks (CD tensile matters for label dispensing).
Related terms
- Burst strength (Mullen)Burst strength is the pressure required to rupture a paper or board sample, applied through a rubber diaphragm by a Mullen tester. It is reported in psi or kPa and is one of the oldest standardised paper strength tests.
- Edge crush test (ECT)ECT measures the edgewise compressive strength of a corrugated board, reported in pounds per inch or kN/m. It is the standard predictor of stacking strength and has largely replaced burst strength as the spec for box certification.
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