Silica gel consists of about 99 % of silicon dioxide (SiO2) and is classified as a synthetic polar and hydrophilic desiccant. It possesses due to its high porosity, a large internal surface area of up to 800 m2/g.This enables a very high water holding capacity. In adsorber filters silica gel is often added with a color indicator. Color changes indicate the water content and therefore the progress of the loading of the desiccant. According to EU legislation (Regulation EC No 1272/2008) silica gel is not classified as a dangerous substance. It is not subject to classification according to EC Directives (67/548/EEC and 1999/45/EC). Silica gel is not among the health and environmentally hazardous substances.