Activated Alumina

is a highly porous compound with a high surface-area-to-weight ratio, used as a desiccant, working by a process called adsorption. Humidity adheres to the Alumina as air passes through, trapping water molecules so that the air dries and passes through the filter. The process reverses (regenerating the desiccant) when the alumina desiccant is heated to ~200 °C and releases the trapped water.