Paper is hygroscopic, which means that it is very susceptible to changes
in relative humidity (RH). For optimum printing and paper storage
conditions the humidity should be kept between 50-60%RH.
Static build-up, web breaks and paper curl are all problems caused by
dry air in the printing industry. By humidifying the atmosphere around
printing presses, reel stand areas and paper stores, problems like these
can be efficiently reduced. Changes in humidity will cause the physical
dimensions of the paper to change which results in misregistration of colors in multi-pass jobs.