Plant fibres are the main raw material used in paper. It is hygroscopic material with a direct relationship to the moisture content of ambient air. Paper absorbs or emits moisture until an equilibrium is achieved between paper and air.

For example, air extracts moisture from paper if room air is relatively drier than the paper stored in it. This is the simple mechanism of drying. Where drying out of stored paper should be avoided, one merely must ensure that a balance is maintained between the moisture content of the air and the desired moisture content of the stored paper.

The moisture content of paper also depends on the type of raw materials used. Mechanical wood pulp absorbs more moisture than chemical pulp, with high-quality paper raw materials like cotton and linen indicating the lowest absorbtion levels.

Ideal air humidity ensures enhanced register accuracy, consistent print quality and, consequently, reduced waste. Unpleasant consequences of inadequate or excessive air humidity include paper distortion, limited machine cycles and the associated additional costs.

Recommended air humidity values in the paper and print industry