Tam/WB2TT wrote:
. . . I once used 3/8 inch Poly something rope. It rotted so badly that
after 6 months I could pull it apart between my two hands. . .

That would have been polypropylene, widely sold in hardware and DIY
stores. It rots in no time if exposed to UV. Polyester holds up very
well, and nylon is just about as good. (I think most of the rope sold
specifically for antenna use is polyester.) I'd use black rope if I
lived in an area having a lot of direct sunlight and/or one that's at at
high elevation, since this improves its UV resistance, but ordinary
nylon or polyester rope lasts many years at my western Oregon QTH.
(Maybe the moss/algae growth helps.) I like nylon because its
stretchiness acts as a shock absorber, but this would be a disadvantage
for some applications.

Roy Lewallen