Moisture Content is the amount of water contained in paper expressed as a percentage of the paper’s total weight. The primary constituents of paper, fibers of cellulose, have a strong affinity for water, and will gain (or lose) it readily, depending on the amount of moisture in the air, or the relative humidity of the surrounding environment. This hygroscopic characteristic of paper makes it dimensionally unstable, as the length and/or width of a paper can change depending on how much water the paper has gained or lost. The moisture content of paper also affects its various mechanical, surface, and electrical properties, and contributes to the qualities of printability and runnability in the various printing processes.
Generally, a range of 3% to 7% is average for the moisture content present in paper stock.