Silica gel is a hard glass-like spherical bead of porous silicone dioxide. Its affinity for water makes it useful as a desiccant (drying agent) in a wide range of applications, from humidity control in product packaging and confined spaces (e.g. safes, closets), to tank breathers for hydraulic oil in power transformer applications, to compressed air and gas drying. Several types of silica gel are available.
Blue indicating beads are deep cobalt blue when dry and turn pink when saturated. This type is commonly used in compressed air and gas drying applications, as well as for tank breathers. The color indicator is cobalt chloride, a carcinogen. Blue indicating silica gel should be avoid in food, pharmaceutical, and other applications where human ingestion may occur.
Orange indicating beads are best for applications where color change is desired and the material may be exposed to food or medicine. These beads turn light green when saturated.
White non-indicating silica gel beads contain no color indicator Typical applications include humidity control in packages and containers and moisture control in safes, closets, and other spaces. White silica gel is less expensive than indicating types and may be mixed with either blue or orange types to achieve humidity indication.