Montmorillonite clay is a naturally occurring mineral that is an inexpensive and nonhazardous desiccant commonly used for humidity control in industrial applications. It adsorbs water vapor easily and does not swell, but has a low ceiling temperature and will begin to desorb moisture at 120 degrees Fahrenheit. Desiccants work best combined with moisture barrier bags, which have moisture vapor transmission ratings indicating how much moisture can penetrate the material over 24 hours.