Silica-gel desiccant；Montmorillonite desiccant
Silica gel is a granular, vitreous, porous form of silicon dioxide made synthetically from sodium silicate. Silica gel contains a nano-porous silica micro-structure, suspended inside a liquid. Most applications of silica gel require it to be dried, in which case it is called silica xerogel. As a desiccant, it has an average pore size of 2.4 nanometers and has a strong affinity for water molecules.
The individual crystals of montmorillonite clay are not tightly bound hence water can intervene, causing the clay to swell. The water content of montmorillonite is variable and it increases greatly in volume when it absorbs water. Chemically, it is hydrated sodium calcium aluminum magnesium silicate hydroxide Al2O3·4SiO2·nH2O.