A paper property that measures its ability to withstand a bending force. Paper has two basic varieties of stiffness: flexural stiffness, which is a paper's resistance to an externally-applied bending force, and handling stiffness, which is a paper's ability to support its own weight. Thickness (or caliper) and basis weight are the chief determinants of a paper's stiffness; generally, a paper's stiffness varies as the cube of thickness (a doubling of caliper produces an eight-fold increase in stiffness). A paper's stiffness is also greater when the bending force is in the cross-grain direction, often by a ratio of two-to-one. The degree of stiffness required varies according to end use requirements.