Jute should work fine.

Sissal would also work, though you will have to cover the fingerloop unless you like blisters on your fingers.

Hemp would probably be the best, as it is strong yet soft on the hands.

Nettle or bamboo fibres should yield a good sling.

Cotton will work so long as you rub the individual yarns in beeswax before starting, otherwise cotton twine can 'fuzz' up.

To be honest though, you should just do some experimenting. That is probably what everyone else does around here in order to find what works for them.

If you are interested in colours, you can dye sissal yourself.

I have used food dye in the past, just soak the twine in a cup of hot water with a teaspoon of salt and add a few drops of food dye into it and using a chopstick or a spoon, stir the dye and salt and leave it for a day. I don't see why you couldn't do the same with cotton or hemp twine.

It seems to work great, though I'm not sure if it would be 'colour fast'... but since I never plan on washing my sling ever again, I don't really care about that aspect.

If you ever get into more complex styles of braiding (Andean Fist-braiding etcetera), go for wool or alpaca. You can get all the colours of the rainbow out of wool and alpaca. If you care about stiffness, go more for Alpaca as it is less stretchy. It is more expensive though.

TheJackinati wrote on Apr 4^th, 2019 at 4:44am:

This

Edit: for the record Jute is my favorite natural fiber to work with.  It's easy on the hands, easy to work with, cheap as dirt, reasonably durable, and makes a good looking sling. I do like the others mentioned also.  Cotton butcher string makes a pretty nice sling.