I start with rigilene boning and a piece of lycra. The rigilene should be about an inch longer than the final circumference you want the bangle to be, and I cut my lycra about an inch longer than that so I have excess at the ends. I cut mine to be about 10" long, if I am remembering correctly off the top of my head. I actually just take the piece of rigilene and make a loop and shove my hand through it, checking to make sure it can actually get over the widest part of my palm. If I'm making multiple I'll then use the first cut piece as my template for the others. I cut my piece of lycra about 3.5-4 times as wide as the piece of rigilene, so I've got wiggle room.