The line to which you refer is most likely an Ultima line called Enigma Super Snood. It comes in black, which they call "silt" and "sand" which is a sort of green colour. I have a number of spools of it in different breaking strains which I got from the UK where it is freely available. Whether the Ultima rep in NZ has it yet I do not know.

What I do know is that it is amazing stuff. You just have to play with a bit of it to see that it is nothing like a normal nylon. (I saw somewhere on the internet that it has magnesium oxide in it). When I rig up the tail half of a pilchard bait I use 2 hooks. The keeper hook is attached with a combination of a half hitch round the tail and 3 wraps of the line round the shank of the hook. Its complicated to describe but anyway a regular nylon trace ends up horribly kinked to the point where it has to be discarded after use a couple of times. No problem now with Ultima Enigma.

I generally use 30 and 40lb bs and it knots up really tight. I also got a spool of about 70 lb bs with the idea of using it for making pulley rigs and using for leaders - mistake. The thicker line does not pull up into tight knots.

About 10 years ago I tried some stuff called Sunset Amnesia 40lb - I am looking at the spool right now. I tried it for leaders and backbones for pulley rigs. I found it had plenty of "memory" when it was pulled off the spool and after a little bit of use the nylon went white and curly like a pigs tail. If it was still available I would avoid it.