Silica gel is an amorphous and porous form of silicon dioxide (silica), consisting of an irregular tridimensional framework of alternating silicon and oxygen atoms with nanometer-scale voids and pores.

Silica gel’s high specific surface area (around 800 m²/g) allows it to adsorb water readily, making it useful as a desiccant (drying agent). Silica gel is often described as “absorbing” moisture, which may be appropriate when the gel’s microscopic structure is ignored, as in silica gel packs or other products. However, material silica gel removes moisture by adsorption onto the surface of its numerous pores rather than by absorption into the bulk of the gel.