Hi, Lupis!
Regarding Balearic slings:
We had a fascinating discussion with a guy named Vicente, who is a member of the Federacio Balear de Tir de Fona (or, the Balearic Slinging Federation). He gave us a lot of information about how slinging is done in Mallorca and the other Balearic Islands.
Balearic slings are basically split-pouch slings (often with a bit of leather covering the pouch cords), made from grasses or other vegetable fiber. Here is a link to a page illustrating
how to braid a Balearic sling
, from start to finish. The text is either Catalan or Spanish (I cannot tell), but the pictures are pretty clear.
Also, here is a page illustrating
a recommended slinging style
. I cannot tell whether this is supposed to be an underhand or overhand style, just from the pictures. Perhaps the text makes it clear, but I cannot read it.