An important consequence of the sorption and de-sorption of water by paper is the change in dimension that usually accompanies changes in moisture content. Such changes in dimension may seriously affect register in printing processes and interfere with the use of such items as tabulating cards. Uneven dimensional changes cause undesirable cockling and curling. Dimensional changes in paper originate in the swelling and contraction of the individual fibers. It has been observed that cellulosic fibers swell in diameter from 15 to 20% in passing from the dry condition to the fiber saturation point.

It is impossible to be precise about the degree of this swelling because paper-making fibers differ considerably in this property, and because the irregular cross-section of fibers creates difficulty in defining diameter. Change that occur in the dimensions of paper with variation in the moisture content is an important consideration in the use of paper. All papers expand with increased moisture content and contract with decreased moisture content, but the rate and extent of change vary with different papers.