At Seascape Marine, we offer pre-cut Laser / ILCA mainsheets. Our favourite option, and the one we use for racing, is Rooster's 6mm Polilite mainsheet, cut to an optimal length. There is no better option out there if you're looking for a high-quality line.
Rooster's 6mm Polilite sheet is a very popular non-twist line, typically used for load-bearing situations, such as mainsheets and spinnaker sheets. With a load bearing outer construction that grips a lightweight inner core, the risk of a bad mainsheet tangle is greatly reduced during moments where you want to make sure you have a smooth release!