A leading edge inflatable kite (LEI) is a single skin kite with inflatable bladders providing structure. It is useful as a power or traction kite. These kites are flown using 2, 4 or 5 control lines and a bar. (See also: kite control systems) A LEI is a great kite for water use because the inflated bladders cause it to float on the water surface. A LEI can sit on the water for an indefinite time and still be relaunched because, unlike a foil kite, there are no chambers that can fill with water. Generally used for kitesurfing and kiteboarding, leading edge inflatable kites come in many different sizes, most commonly from 5 to 18 square metres.