Moisture content refers to the water containing in soft contact lenses, as a percentage of the weight of the lens, for example, the lens moisture content of 50%, means the half of the weight of the lens is moisture. The moisture content of soft lenses generally between 38 % to 78%, the higher the water content of the product said the better oxygen permeability, but the thickness of lens will also be increased. Contact lens manufacturers usually use high moisture content or ultra-thin lenses to improve the oxygen permeability of the lens. But in any case, USKO recommends that customers should not wear soft lens more than fourteen hours a day , and should not wear lens during sleep.