Relative humidity
Relative humidity (RH) is the measure of the humidity, or the water vapor content, in relation to the atmosphere and ranges from damp to dry. Material properties determine the affect that different levels of RH can have on any particular item. Organic materials like wood, paper, and leather, as well as some inorganic material like metals are susceptible to damage from incorrect RH. Damage ranges from physical changes like cracking and warping of organic materials to chemical reactions like corrosion of metals. Temperature has a direct effect on relative humidity: as warm air cools, relative humidity increases and as cool air warms up, relative humidity falls. Dampness can cause the growth of mold which has its own damaging properties. Research in the field has determined the various ranges and fluctuations of incorrect humidity, the sensitivity of various objects to each one, and has helped establish guidelines for proper environmental conditions specific to the objects in question.