A defect in paper or board, appearing as a
curvature in the sheet, caused by "two-sidedness"
of the sheet, which results in unequal shrinkage
between the felt and wire sides when the paper or
board is subjected to changes in relative
humidity. In addition, fiber orientation has an
influence on the direction and magnitude of curl.
The result of curl is the tendency of the paper or
board to form a tube (curl)) at the edges, the
axis of which is parallel to the machine direction
of the material. (17
, 42 , 98 )