Whatever you do, do NOT get stuff from
Robline. It is greasy and twists like crazy. The finished whipping will look fine, but it sure is hard to pull the needle through when your hands are all greasy!
The best I've used is
Marlow. I recommend size #4 for HRC, Beeline and any other arborist climbing application. I don't usually use the heavier stuff until I get to the bigger rigging lines.
I have also used some stuff from a company called
Liros. I got it off ebay and it was as good as Marlow. However, I can't find it in the US. Oh, it was only available in white.
I've used several other no-name whipping twines and they have all been good. Just stay away from Robline.
I used to get Marlow Whipping twine from West Marina on North in Chicago. 312-654-1818
love
nick