What I did with my Ursack was asked Tom Cohen for where he got the bearproof rope and I ordered a longer length from his same supplier and replaced the rope — this allowed me to tie the bag to a boulder (instead of a tree). I also have a Bearikade (because for 1/2 year the Ursack was not even conditionally approved and I had gotten the Bearikade during that time). The weight difference is about the same when you factor in the liner, extra length rope. the rope is a spectra rope from I believe Western Marine — I think it is 5/32" thick rope, I forget. I can find the email from Tom if anyone is interested.
I found Tom's note: " You can buy it from West Marine or similar stores. We use New England Ropes T 100 in 5/32."
I got the rope at Western Marine online – "T-100 Technora-Spectra Double Braid" by New England Ropes.
T-100 5/32”, 2,300lb Breaking Strength 3474723 (WM Model), 2850-05-00900 (MFG Part #).