Desicant

A desiccant or humectant is a <a href="http://en.wikipedia.org/wiki/Hygroscopic" title="Hygroscopic" class="mw-redirect" >hygroscopic</a> substance that induces or sustains a state of dryness (<a href="http://en.wikipedia.org/wiki/Desiccation" title="Desiccation" >desiccation</a>) in its local vicinity in a moderately well-sealed container.

Commonly encountered pre-packaged desiccants are solids, and work through <a href="http://en.wikipedia.org/wiki/Absorption_(chemistry)" title="Absorption (chemistry)" >absorption</a> or <a href="http://en.wikipedia.org/wiki/Adsorption" title="Adsorption" >adsorption</a> of <a href="http://en.wikipedia.org/wiki/Water" title="Water" >water</a>, or a combination of the two. Desiccants for specialized purposes may be in forms other than solid, and may work through other principles, such as chemical bonding of water molecules.

Pre-packaged desiccant is most commonly used to remove excessive <a href="http://en.wikipedia.org/wiki/Humidity" title="Humidity" >humidity</a> that would normally degrade or even destroy products sensitive to moisture. Some commonly used desiccants are: <a href="http://en.wikipedia.org/wiki/Silica_gel" title="Silica gel" >silica gel</a>, <a href="http://en.wikipedia.org/wiki/Activated_charcoal" title="Activated charcoal" class="mw-redirect" >activated charcoal</a>, <a href="http://en.wikipedia.org/wiki/Calcium_sulfate" title="Calcium sulfate" >calcium sulfate</a>, <a href="http://en.wikipedia.org/wiki/Calcium_chloride" title="Calcium chloride" >calcium chloride</a>, <a href="http://en.wikipedia.org/wiki/Montmorillonite_clay" title="Montmorillonite clay" class="mw-redirect" >montmorillonite clay</a>, and <a href="http://en.wikipedia.org/wiki/Molecular_sieve" title="Molecular sieve" >molecular sieves</a>.

A specific usage of a desiccant would be in <a href="http://en.wikipedia.org/wiki/Insulated_glazing" title="Insulated glazing" >insulated windows</a> where it is placed inside the spacer between the air space and window edge. This prevents moisture condensation between the panes.