As a sorbent (insoluble materials) it is used to recover liquids through the mechanism of absorption, or adsorption, or both. Absorbents are materials that pick up and retain liquid distributed throughout its’ molecular structure causing the solid to swell (50% or more). The absorbent must be at least 70% insoluble in excess fluid. Adsorbents are insoluble materials that are coated by a liquid on its’ surface, including pores and capillaries, without the solid swelling more than 50% in excess liquid. To be useful in combating oil spills, sorbents need to be both oleophilic (oil-attracting) and hydrophobic (water-repellent). Natural inorganic sorbents such as perlite can adsorb from 4 to 20 times their weight in oil. The characteristics of both sorbents and oil types must be considered when choosing sorbents for cleaning up oil spills: Rate of absorption – The absorption of oil is faster with lighter oil products. Once absorbed the oil cannot be re-released. Effective with light hydrocarbons (e.g. gasoline, diesel fuel, benzene).