Well, it's taken me almost a year but I've finally finished THIS:
https://www.amazon.co.uk/Homecraft-2-5-Twine-Sisal-Ball/dp/B01IPLZR1M/ref=pd_sim...That is a 2.5kg football sized ball of sisal containing ~750m of twine. If using 35m for each sling that's over 21 slings!
Since I've just used the last of it now, it seems a fitting time to reflect on it as probably my favourite natural material.
For me sisal has to be soaked in water to make nice feeling slings (though thinner slings can survive without). This completely removes any 'stiffness' from the cords leaving them remarkably pliable (I couldn't believe it first time I did it).
One potential problem is that soaking sisal can introduce an undesirable amount of stretch into the cords. To minimize this you can dry the sling under stretch, or wrap it round a cylinder tightly (I use a foam roller) I've found this significantly reduces stretch.
Sisal is famously rough on hands, so I also heavily recommend a leather lined fingerloop for maximum comfort.
What do you get for all this effort?
Well, your sling is not gonna break anytime fast for one. That's probably why I like it so much. Aside from general durability- If your sling is built for cracking sisal will outlast most natural fibres which disintegrate in no time at all.
Disadvantages-
-Your hands won't like you initially
-Only one colourscheme
-Slings can be a bit 'springy' I find it a nice feel but some might not
Time to order another football