oh boy, plastic bag slings
Plastic bags were one of my first attempts at making slings and is actually one of my favorites(just because virtually ANYWHERE you go on this planet, you'll always eventually reach some sort of plasic bag...).
I have never tried fusing bags, just cut the bag into circular strips, then interlace them to form one longer strip. There is a diagram below that explains it well... Can make a fragile long cord in no time whatsoever.
Take 3 of these and braid them, you'll find that they're quite strong when finished
Laying the Circular strips down
Second Step
Third Step
Pull Slowly and it'll tighten real nice, if you break it just break it near the longer one and try it again.
Works great to be used for braiding or even making cordage.
I gotta see if I can find my old pics of my crocheted plastic bag sling... hmmmm