Water content is an important feature of the various plastics used to make soft contact lenses. As a general rule, with conventional soft contact lenses, the higher the water content of the lens, the more oxygen can pass through the lens to the surface of the eye. This is important for lens comfort and healthy eyes - but high water content lenses may be more fragile, so are more likely to tear with frequent handling. The relationship between water content and oxygen transmission is not the same with lenses made from silicone hydrogel materials which achieve very high levels of oxygen transmission regardless of their water content.