Here's a Youtube about Plarn
https://www.youtube.com/watch?v=gQwTcizA7Oo
I almost always sit with my knees pulled up. When I make plarn it comes in handy because I'll lean one of them into the edge of my desk and that helps me stabilize the loops when putting them together.
After I loop together enough bags that it piles up at my feet, lol, I make a ball out of the plarn then just add to the ball as I continue.
I just did find this
https://www.youtube.com/watch?v=MQtcpPBJc70 video. She does it differently so I guess there's no hard rule to making plarn. My loops tend to be slightly thinner than an inch.
It is VERY time consuming but something a little different to play around with when I get tired of regular crocheting.