I use 5/16 Dynema with the covers stripped off 15' for my spin sheets on my 34 footer. The stripped portion weighs next to nothing and are strong enough carry the sail in winds over 20kts. If the winds go light, I unshackle the lazy guy which mostly does the trick. If the winds are really light, I bought some ¼ Dacron (sta-set?) for my dental floss. But frankly, at those wind speeds, the weight of ¾ oz kite is more of an issue than the line weight. Some day I'll get get me a ½ oz runner.