Stiffness

Stiffness measures how much force is required to bend a paper strip to a given angle. The Taber method bends a 38 mm strip to 15° and reports the force in Taber units. The L&W method bends to 5° and reports bending moment in mN·m.

Stiffness scales with the cube of caliper and the square of modulus. For cartonboard converters, stiffness at a given grammage is the single most important purchasing spec, because it determines whether the carton keeps its shape on the retail shelf.