Important rope characteristics for a spinnaker and gennaker sheet are: light weight, good grip and flexibility. In particular for yachts up to 36 ft there is a lot of manual trimming requiring good grip and flexible ropes. With very low winds the rope weight should not easily pull your spinnaker or gennaker down.
For cruising we recommend polyester for spinnaker and gennaker sheets, usually in smaller diameters than the genoa sheet. If you want a step up, choose for sheets with a core of Dyneema®. These are more lightweight. To further save weight the cover is sometimes removed in the area between winch and the spinnaker.
Suggested length, click here
Suggested diameter, click here