The resistance to bending is an important property of paper and board, and perhaps the most important property of packaging papers and solid boards. The majority of standards refer to 2-point methods for measuring bending resistance, of which many can be performed at Smithers.

Bending resistance is also a key property of corrugated board, for which the preferred methods use a four-point test geometry (see corrugated board stiffness below).

2-point bending stiffness 

The stiffness of paper and solid board is measured using a Smithers Board and Crease Stiffness Tester (CBT2). The 2-point bending stiffness of paper and paperboard can also be determined by Smithers using Kenley, L&W and Taber instruments. The results are quoted in mN (bending resistance) or mNm (bending moment).

Smithers is UKAS, ISO 17025 accredited for these test methods. The instruments we used satisfy the requirements of British Standard BS 3748 and International Standard ISO 2493.

Corrugated board stiffness

The amount of panel bulging needs to be limited if a case is to perform its function in a vertical stack. The arrangement for testing the bending stiffness of corrugated boards uses the four-point method.

Clarke stiffness

Clarke stiffness measures the stiffness as the free length in centimetres of a paper strip which bends under its own weight. Clarke stiffness is measured in accordance with Tappi T451.

Resonance stiffness

The resonance method works on the principle that the natural vibrating frequency of a material is related to its bending stiffness. Smithers use an Adamel L'Homargy (Kodak Pathe) instrument to measure the resonance stiffness of paper in accordance with International Standard ISO 5629.

The Taber Stiffness, Clarke stiffness, and Resonance Stiffness testing methods are included in Smithers Paper Proficiency Service.

Smithers offers testing to International Standard ISO 5628 and Tappi T820.

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