The selvage on top and bottom need be strong enough, because it need be installed with the ropes, floats and leads.
There are many kinds of selvage:
1.monofilament line
2.multifilament twine
3.multi-monofilament twine
This video shows the first type, this is most popular type in the market.
For some clients, the colors of the twine means different quality, it is easy for fishermen to idenfy the different quality. All the colors could be customized for you.