When made properly the rope is about as strong as 3/8 nylon rope.
To do this tutorial you will need:
1. Plenty of plastic bags
2. A knife
3. A three strand rope making machine. You can make one out of bike parts, wood, or get an old one off ebay.
4.A paddle with three arms - a crucifix will do
5. A spinner hook
6. Two or three people. One at each end and one in the middle is best.
Step 1: Cut your plastic bags and make a daisy chain
It takes about 4 regular sized shopping bags to make a foot of rope.
I've scavenged most of mine from the grocery store recycle bins. choose stronger bags if you can find them. Bigger bags don't work as well with this method.
The bags I use have a seam down the sides. Lay them on a cutting board in a small pile and cut down the seam. Be careful not to cut the bottom of the bag or it will be much weaker. You should now have a peice of plastic with a loop at each end. When you have cut enough bags you can loop the handles through each other to make a daisy chain. you shouldn't have to tie any knots, but if a bag breaks for some reason it's not a big deal to tie it.
If you can't get a good supply of bags with the seams on the side try poking a hole in the side, near bottom of the bag instead of cutting them down the middle.
If you're not using your chain to make rope right away wrap in in a spool around a stick to keep it from getting tangled.