I recently tested inner tubing from bikes, not a very good slingshot band material. Unstretchy and slow.
But now I learned that until WW2, inner tubings were made from natural latex, until the shortages lead to using a material called butyl rubber as a substitute. That substitude was then kept to this day.
Except that some high end guys are using latex again, simply because they believe that it is lighter and has less rolling resitance.
Read about the inner tubing history here
So I bought the best stuff I could find (a whole 28" tubing set weighs less than 60 gramms = 960 gr) and it arrived today!
I immediately checked it out and it is VERY PROMISING. It stretches more far than TB Gold (about 65%) and feels more linear until the very end of the stretch. I banded a Panther up with 15cm effective draw, untapered. 5 kg draw! And fast. Probably the fastest tubular rubber I ever tested.
As soon as I have some time, I will make a tapered butterfly set and test the heck out of it.