Cellulose fibers (main constituent of paper) swell in diameter from 15 to 20% from dry condition to saturation point. Since most of the fiber in paper sheet are aligned in the machine run direction, absorption and de-absorption of moisture by paper causes the change in CD dimension. 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 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 occurs 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 changes vary with different papers.
Dimensional stability of paper can be improved by avoiding fiber to absorb moisture. Well sized papers have better dimensional stability.
| Typical Values | ||
| Grade | MD (%) | CD (%) |
| Carbonless Paper | 0.050-0.150 | 0.200-0.400 |
| Bond Paper | 0.100-0.200 | 0.200-0.400 |
| Coated Art Paper (under 200 g/m2) | 0.090-0.150 | 0.150-0.350 |
| Gasket Paper | 0.400-1.000 | 0.500-1.100 |
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