Flying lines are made of a very strong material, frequently Ultra high molecular weight polyethylene, in order to handle the dynamic load in unpredictable wind while maintaining a small cross-sectional profile to minimize drag. They come in sizes generally between seven and thirty-three meters; experimentation with line lengths is common in kiteboarding. The lines attach the rider's control bar to the kite using attachment cords on the kite edges or its bridle. Most power kites use a 3, 4 or 5-line configuration. The 5th line is used to aid in water re-launching or adjusting the kite's angle of attack. (source Wikipedia)