Sinkline with extra strength and durability.
Sinkline is flexible, strong and easy to handle made of 50% polyester and 50% danline/polysteel. Sinklines are widely used in lobster and crab fisheries. This line is then attached between the guard (buoy/ball) and the lobster or crab line.
The advantage of a sinkline over a pure polyester line, or polypropylene line for that matter, is that the vacuum line treviflex is more tightly wound. It is also more dimensionally stable because it is more heavily beaten. Of course, the rope is maximally UV-treated for many years of outdoor use. Line sinks in water.