What is Hygroscopic Material?
A hydroscopic material is one which readily takes up and retains moisture. As the humidity increases, hygroscopic materials take on more and more water until they reach equilibrium with the environment. This increases substantially above 60%Rh. If water evaporates too quickly into warm interior air without a corresponding humidity reduction, the result increases the chance for microbial growth, thus damaging hygroscopic materials. Therefore, hygroscopic materials, previously undamaged by liquid water, can become damaged if the humidity is not controlled. This is referred to as secondary damage and is what occurs when air movers, which increase the rate of evaporation (adding humidity), are placed without setting up an adequate dehumidification capacity. The humidity will rise rapidly and can cause secondary damage to hygroscopic materials. A very important point is that the rate of evaporation is directly proportional to the vapor pressure differential between the surface of wet materials and the adjoining air. This indicates that the capacity for dehumidification should actually exceed the rate of evaporation. This "abnormally dry" air mass insures an even greater rate of evaporation.